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In biology, the series of changes that the members of a species undergo as they pass from the beginning of a given developmental stage to the inception of that same developmental stage in a subsequent generation.


1. Astron. A circle or orbit in the heavens.

1631 R. BRATHWAIT Whimzies 13 Horizons, Hemispheares..Astrolabes, Cycles, Epicycles, are his usuall dialect. 1667 MILTON P.L. VIII. 84 How gird the Sphear With Centric and Eccentric scribl'd o're, Cycle and Epicycle, Orb in Orb. fig. 1831 CARLYLE Sart. Res. III. viii, What infinitely larger Cycle (of Causes) our little Epicycle revolves on.

2. a. A recurrent period of a definite number of years adopted for purposes of chronology. (See quot. 1788.) cycle of indiction: see INDICTION.

Metonic or lunar cycle: a cycle of 19 years, established by the Greek astronomer Meton, and used for determining the date of Easter. solar cycle: a period of 28 years, at the end of which the days of the week (according to the Julian Calendar) recur on the same days of the month.

For lessons on the topic of Cycles, follow this link.

1387 TREVISA Higden (Rolls) VII. 271 The dissonaunce of {th}e cicles of Dionise the lesse ageyne the trawthe of gospelles. 1398 {emem} Barth. De P.R. IX. iv. (1495) 349 The Cycle and course of the mone conteyneth twelue comyn yeres and seuen yeres Embolismalis. c1425 WYNTOUN Cron. IX. xxiii. 5 {Edh}e cikil of our Salvatioune {Edh}at is {th}e Annuntiatiowne. 1646 SIR T. BROWNE Pseud. Ep. IV. xii. 211 Of months, of years, Olympiades, Lustres, Indictions, Cycles, Jubilies, &c. 1656 BLOUNT Glossogr. s.v., This revolution is called the Cycle of the Sun, taking name from Sunday, the letter whereof (called therefore Dominical) it appoints for every yeer. 1788 PRIESTLEY Lect. Hist. III. xiv. 111 The greatest difficulty in chronology has been to accommodate the two methods of computing time by the course of the moon and that of the sun to each other..This gave birth to many cycles in use among the ancients. 1844 LINGARD Anglo-Sax. Ch. (1858) I. i. 47 The Roman church, about the middle of the sixth century, adopted a new cycle, which had been lately composed by Dionysius Exiguus...But the British churches..continued to use the ancient cycle.

b. gen. A period in which a certain round of events or phenomena is completed, recurring in the same order in succeeding periods of the same length.

1662 PETTY Taxes 24 The cycle within which dearths and plenties make their revolution. 1795 BURKE On Scarcity Wks. VII. 379 Wages..bear a full the medium of provision during the last bad cycle of twenty years. 1836 J. H. NEWMAN in Lyra Apost. (1849) 185 The world has cycles in its course, when all That once has been, is acted o'er again. 1867 FREEMAN Norm. Conq. (1876) I. iii. 96 One of those curious cycles which so often come round in human affairs.

c. A long indefinite period of time; an age. 1842 TENNYSON Locksley Hall 184 Better fifty years of Europe than a cycle of Cathay. 1851 MAYNE REID Scalp Hunt. xix, After many years{em}ages, centuries, cycles perhaps.

3. a. A recurrent round or course (of successive events, phenomena, etc.); a regular order or succession in which things recur; a round or series which returns upon itself.


1664 EVELYN Kal. Hort. (J.), To present our gardeners with a complete cycle of what is requisite to be done throughout every month of the year. 1691 WOOD Ath. Oxon. II. 824 The Caroline Cycle [for the election of Proctors] being still kept back a year. 1861 M. PATTISON Ess. (1889) I. 47 A committee of nine members, in which every Hanse town was in its turn represented, according to a fixed cycle. 1875 LYELL Princ. Geol. II. III. xxxvii. 329 The whole cycle of changes returns into itself, just as do the metamorphoses of an insect.

b. Physics, etc. A recurring series of operations or states, spec. in internal combustion engines. Also, short for cycles per second (abbrev. C.P.S., cps., c/s), the unit of frequency of an oscillation (as an alternating current, a sound wave, etc.).

a1884 KNIGHT Dict. Mech. Suppl. 382/2 The complete cycle of motions in the Otto engine is accomplished only by two complete revolutions of the working shaft, or four strokes of the piston. 1887 Encyl. Brit. XXII. 479/2 Generally in heat-engines the working substance returns periodically to the same state of temperature, pressure, volume, and physical condition. When this has occurred the substance is said to have passed through a complete cycle of operations. 1893 T. O'C. SLOANE Standard Electr. Dict. 175 Cycle of alternation, a full period of alternation of an alternating current. It begins properly at the zero line, goes to a maximum value in one sense and returns to zero, goes to maximum in the other sense and returns to zero. 1920 Whittaker's Electr. Engineer's Pocket-Bk. (ed. 4) 348 In the early days, when electricity was used only for lighting, frequencies round about 100 cycles were usual. 1929 A. F. COLLINS Aviation 148 After the power stroke is completed three more strokes must take place before there is another explosion stroke and, hence, another power stroke. Then the series of strokes, or cycle, as it is called, begins all over again, and this is what is meant by a four-stroke cycle engine. 1940 Chambers's Techn. Dict. 206/1 C.P.S., cps., c/s, abbrevs. for cycles per second, the usual measure of frequency. 1944 A. WOOD Physics of Music iv. 42 The lowest frequencies used in the orchestra are those of the double bass and the bass tuba, which lie between 60 and 80 cycles per second... Tones of male speech embrace a range of from 120 to 8000 c.p.s. 1959 Consumer Rep. (N.Y.) Sept. 452/2 Only one [tweeter] provided adequate and relatively uniform power in the high-frequency range to beyond 20,000 cps. 1965 Electronics Weekly 10 Mar. 22/5 It operates from a standard single phase 50 c/s supply. 1967 Electronics 6 Mar. 325/1 Markus continues to use ‘cycles per second’ instead of ‘hertz’.

c. Geology. cycle of erosion, sedimentation (see quots.).

1904 CHAMBERLIN & SALISBURY Geol. (1905) I. iii. 78 It has now been seen that by whatever method erosion by running water proceeds..the final result of subaërial erosion must be the production of a base-level... The time involved in the reduction of a land area to base-level is a cycle of erosion. 1921 L. D. STAMP in Geol. Mag. LVIII. 109 A ‘cycle of sedimentation’ comprises the deposits of a complete oscillation of the basin, each oscillation including a positive phase of marine invasion and a negative phase of regression. 1960 {emem} Britain's Struct. & Scenery (ed. 5) vii. 70 As the cycle of erosion progresses..features which are due to varying resistance of the rocks..gradually become eliminated as the surface is reduced to a monotonous level..plain.

4. gen. A round, course, or period through which anything runs in order to its completion; a single complete period or series of successive events, etc.

1821 SHELLEY Adonais xxvii, Or hadst thou waited the full cycle, when Thy spirit should have filled its crescent sphere. 1845-6 TRENCH Huls. Lect. Ser. I. iv. 66 The cycle of God's teaching is complete. 1869 J. MARTINEAU Ess. II. 230 Doctrines which have run their cycle.

5. A complete set or series; a circle, a round.

1662 EVELYN Chalcogr. Bb, To compile, and publish a Compleat Cycle and Hystory of Trades. 1678 WOOD Life (Oxf. Hist. Soc.) II. 401 Vide the printed cycle for names of collectors and how many admitted. 1829 SCOTT Demonol. iv. 121 [He] figures among a cycle of champions. a1836 GODWIN Ess. (1873) 217 The most intolerable sentence in the whole cycle of religious morality.

6. spec. A series of poems or prose romances, collected round or relating to a central event or epoch of mythic history and forming a continuous narrative; as the Arthurian cycle. Also transf. Originally used in the Epic cycle [Gr. {oasper} ({elenis}{pi}{iota}{kappa}{gograve}{fsigma}) {kappa}{guacu}{kappa}{lambda}{omicron}{fsigma}], the series of epic poems written by later poets (Cyclic poets) to complete Homer, and presenting (with the Iliad and Odyssey) a continuous history of the Trojan war and of all the heroes engaged in it.

1835 THIRLWALL Greece I. vi. 248 They..formed the basis or nucleus of the epic cycle. 1837 Penny Cycl. IX. 470/1 Those cycles of metrical romances which have for their subjects the exploits of Alexander the Great, King Arthur, and other heroes. 1870 SWINBURNE Ess. & Stud. (1875) 66 The marvellous opening cycle of twenty-eight sonnets. 1873 H. MORLEY First Sk. Eng. Lit. 61 The cycle of the Charlemagne romances..those of the Arthurian cycle. 1874 H. R. REYNOLDS John Bapt. i. §6. 56 The mythopoeic faculty has not engendered a cycle of miracles around the simple story.

7. Med. [L. cyclus.] With the ‘methodic’ physicians: A course of remedies, hygienic and medicinal, continued during a fixed series of days.

1882 Syd. Soc. Lex. s.v. Cyclus, Cælius Aurelianus distinguished three kinds of cycles or periods..The cycle was resumed several times if needed.

8. Bot. A complete turn of the spire recognized in the theory of spiral leaf-arrangement.

1857 HENFREY Bot. 41 The series of leaves included by the spiral line in passing from the first leaf to that which stands directly above it is called a cycle.

9. Zool. In corals, a set of septa of equal length.

1877 HUXLEY Anat. Inv. Anim. iii. 164 The septa in the adult Hexacoralla..of the same lengths are members of one ‘cycle’; and the cycles are numbered according to the lengths of the septa, the longest being counted as the first. In the young, six equal septa constitute the first cycle.

10. Math. a. Geom. A closed path in a cyclic or multiply-connected region. b. (See quot. 1893.)

1881 MAXWELL Electr. & Magn. I. 16 Every new line completes a loop or closed path, or, as we shall call it, a cycle. 1893 FORSYTH Theory of Functions 593 In the theory of Substitution-Groups the set of homologous corners of a given region is called a cycle.