cryptogram (n.)

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).

also gramme, metric unit of weight, 1797, from French gramme (18c.), from Late Latin gramma "small weight," from Greek gramma "small weight," a special use of the classical word meaning "a letter of the alphabet" (see -gram). Adopted into English about two years before it was established in France as a unit in the metric system by law of 19 frimaire, year VIII (1799). "There seems to be no possible objection to adopting the more convenient shorter form, except that the -me records the unimportant fact that the word came to us through French" [Fowler].

1933, "to decode an intercepted message," 1936, "to solve a cryptogram," from de- + cryptogram. Related: Decrypted; decrypting.