before vowels crypt-, word-forming element meaning "secret" or "hidden, not evident or obvious," used in forming English words at least since 1760 (crypto-Calvinianism), from Latinized form of Greek kryptos "hidden, concealed, secret" (see crypt; the Greek combining form was krypho-).

In 19c. often of secret religious faith; from 1870s in scientific words; since c. 1945 typically of hidden political loyalties. Crypto-fascist is attested from 1937; crypto-communist from 1946. Hence, as an abstracted noun, crypto "person who conceals a political adherence" (1946).

word-forming element used in biological and zoological compounds, from Latinized form of Greek ktenidion "a little comb," diminutive of kteis "comb," from PIE root *pekt-en- "comb" (source also of Latin pecten "comb").

before a vowel, cycl-, word-forming element in technical terms meaning "circle, ring, rotation," from Latinized form of Greek kyklos "circle, wheel, ring" (from PIE root *kwel- (1) "revolve, move round"). In organic chemistry it is used in forming chemical names of cyclic compounds.

word-forming element meaning "having a head" (of a specified type), from Greek kephalē "head" (see cephalo-).

representing the common pronunciation of the verbal phrase come on, by 1929. Come on! as an urge to advance or go with is from mid-15c. (see come).