Concealed or secret.
[Greek kruptos, hidden.]
One set of words relates to the production of messages intended only to be understood by the intended recipient, or to methods for illicitly reading them. Text containing such a private message is a cryptogram and the process of creating it is encryption; the art of preparing or reading codes or ciphers is cryptography; the techniques of cracking codes or ciphers to discover messages are collectively called cryptanalysis.
The form also appears in the biological sciences. A cryptogam (Greek gamos, marriage) is a plant that reproduces by spores, so named because the means of reproduction were not obvious at the time; some organisms survive dry conditions through cryptobiosis, in which their metabolic activity becomes undetectably low; cryptozoology is the search for species of animal whose existence is disputed.
A third group has the idea of some membership, allegiance, or belief kept secret, as in crypto-communist, crypto-fascist, or crypto-semite.