secret

adjective

1
not openly made known
a secret marriage
a secret bride
2
the next to highest level of official classification for documents
3
having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding
mysterious symbols
the mystical style of Blake
4
not expressed
secret (or private) thoughts
5
conducted with or marked by hidden aims or methods
clandestine intelligence operations
cloak-and-dagger activities behind enemy lines
6
indulging only covertly
a secret alcoholic
7
communicated covertly
their secret signal was a wink
secret messages
8
(of information) given in confidence or in secret
this arrangement must be kept confidential
their secret communications
9
hidden from general view or use
a privy place to rest and think
a secluded romantic spot

1
something that baffles understanding and cannot be explained
how it got out is a mystery
it remains one of nature's secrets
2
information known only to a special group
the secret of Cajun cooking
3
something that should remain hidden from others (especially information that is not to be passed on)
the combination to the safe was a secret
he tried to keep his drinking a secret

Also useful for “secret”:Unscrambler— Rearrange the letters in “secret”