secret

adj. 1 kept or meant to be kept private, unknown, or hidden. 2 acting or operating secretly. 3 fond of secrecy. n. 1 thing kept or meant to be kept secret. 2 mystery. 3 effective but not generally known method (what's their secret?; the secret of success).  in secret secretly.  secretly adv. [latin secerno secret- separate]

a. Hidden; concealed; as, secret treasure; secret plans; a secret vow.