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 of genius is to carry the spirit of the child into old age, which means never losing your enthusiasm.
Concealed
Part of speech: verb
Definition: To hide something from view or from public knowledge, to try to keep something secret.
Example sentence: For if the mystery concealed of old is made manifest to the Apostles through the prophetic writings, and if the prophets, being wise men, understood what proceeded from their own mouths, then the prophets knew what was made manifest to the Apostles.