1. [n]  a shortened version of `bicycle' or `tricycle' or `motorcycle'
2. [n]  a single complete execution of a periodically repeated phenomenon; "a year constitutes a cycle of the seasons"
3. [n]  a periodically repeated sequence of events; "a cycle of reprisal and retaliation"
4. [n]  a series of poems or songs on the same theme; "schubert's song cycles"
5. [n]  the unit of frequency; one Hertz has a periodic interval of one second
6. [n]  an interval during which a recurring sequence of events occurs; "the neverending cycle of the seasons"
7. [v]  recur in cycles
8. [v]  ride a bicycle
9. [v]  ride a motorcycle
10. [v]  pass through a cycle; "This machine automatically cycles"
11. [v]  cause to go through a cycle

1. \Cy"cle\ (s?"k'l), n. [F. ycle, LL. cyclus, fr. Gr.
   ky`klos ring or circle, cycle; akin to Skr. cakra wheel,
   circle. See {Wheel}.]
   1. An imaginary circle or orbit in the heavens; one of the
      celestial spheres. --Milton.
   2. An interval of time in which a certain succession of
      events or phenomena is completed, and then returns again
      and again, uniformly and continually in the same order; a
      periodical space of time marked by the recurrence of
      something peculiar; as, the cycle of the seasons, or of
      the year.
            Wages . . . bear a full proportion . . . to the
            medium of provision during the last bad cycle of
            twenty years.                         --Burke.
   3. An age; a long period of time.
            Better fifty years of Europe than a cycle of Cathay.
                                                  --Tennyson.
   4. An orderly list for a given time; a calendar. [Obs.]
            We . . . present our gardeners with a complete cycle
            of what is requisite to be done throughout every
            month of the year.                    --Evelyn.
   5. The circle of subjects connected with the exploits of the
      hero or heroes of some particular period which have served
      as a popular theme for poetry, as the legend of Arthur and
      the knights of the Round Table, and that of Charlemagne
      and his paladins.
   6. (Bot.) One entire round in a circle or a spire; as, a
      cycle or set of leaves. --Gray.
   7. A bicycle or tricycle, or other light velocipede.
   {Calippic cycle}, a period of 76 years, or four Metonic
      cycles; -- so called from Calippus, who proposed it as an
      improvement on the Metonic cycle.
   {Cycle of eclipses}, a period of about 6,586 days, the time
      of revolution of the moon's node; -- called {Saros} by the
      Chaldeans.
   {Cycle of indiction}, a period of 15 years, employed in Roman
      and ecclesiastical chronology, not founded on any
      astronomical period, but having reference to certain
      judicial acts which took place at stated epochs under the
      Greek emperors.
   {Cycle of the moon}, or {Metonic cycle}, a period of 19
      years, after the lapse of which the new and full moon
      returns to the same day of the year; -- so called from
      Meton, who first proposed it.
   {Cycle of the sun}, {Solar cycle}, a period of 28 years, at
      the end of which time the days of the month return to the
      same days of the week. The dominical or Sunday letter
      follows the same order; hence the solar cycle is also
      called the {cycle of the Sunday letter}. In the Gregorian
      calendar the solar cycle is in general interrupted at the
      end of the century.
   

2. \Cy"cle\ (s?"k'l), v. i. [imp. & p. p. {Cycled}. (-k'ld);
   p. pr. & vb. n. {Cycling} (-kl?ng).]
   1. To pass through a cycle of changes; to recur in cycles.
      --Tennyson. Darwin.
   2. To ride a bicycle, tricycle, or other form of cycle.
   

3. \Cy"cle\, n.
   (a) (Thermodynamics) A series of operations in which heat is
       imparted to (or taken away from) a working substance
       which by its expansion gives up a part of its internal
       energy in the form of mechanical work (or being
       compressed increases its internal energy) and is again
       brought back to its original state.
   (b) (Elec.) A complete positive and negative wave of an
       alternating current; one period. The number of cycles
       (per second) is a measure of the frequency of an
       alternating current.
   

A basic unit of computation, one period of a computer clock.

Each instruction takes a number of clock cycles. Often the computer can access its memory once on every clock cycle, and so one speaks also of "memory cycles".

Every hacker wants more cycles (noted hacker Bill Gosper describes himself as a "cycle junkie"). There are only so many cycles per second, and when you are sharing a computer the cycles get divided up among the users. The more cycles the computer spends working on your program rather than someone else's, the faster your program will run. That's why every hacker wants more cycles: so he can spend less time waiting for the computer to respond.

The use of the term "cycle" for a computer clock period can probably be traced back to the rotation of a generator generating alternating current though computers generally use a clock signal which is more like a square wave. Interestingly, the earliest mechanical calculators, e.g. Babbage's Difference Engine, really did have parts which rotated in true cycles.

[Jargon File]