Why was "tantrum" trending last week?
before vowels crypt-, word-forming element meaning "secret" or "hidden," used in forming English words since at least 1760, from Latinized form of Greek kryptos "hidden, concealed, secret" (see crypt; the Greek comb. form was krypho-). Crypto-fascist is attested from 1937; crypto-communist from 1946.
crypto- or crypt-
Hidden; secret: cryptogenic.