Secret
Part of speech: noun
Definition: Knowledge that is hidden and intended to be kept hidden.
Part of speech: verb
Definition: To make or keep secret.
Part of speech: adjective
Definition: Being or kept hidden.
Example sentence: The secret was to just be cool, stay in God's graces, and work it out.
Covert
Part of speech: adjective
Definition: Partially hidden, disguised, secret, surreptitious.Covered.
Part of speech: noun
Definition: Area of thick undergrowth where animals hide.
Example sentence: The second is the damage to the credibility and independence of a free press which may be caused by covert relationships with the U.S. journalists and media organizations.