secret
se-cret
adjective
Not known or seen or not meant to be known or seen by others.
"The meeting was held in a secret location."
noun
Something kept hidden or unknown to others.
"I have a secret I can't tell you."
Thesaurus
Synonyms: closed book, enigma, mystery, secluded, private, privy, unavowed, unacknowledged, arcanum, confidential, covert, concealed