(countable) A piece of knowledge that is hidden and intended to be kept hidden.

The key or principle by which something is made clear; the knack.

Something not understood or known.

(uncountable) Private seclusion.

(historical) A form of steel skullcap.

(Christianity, often in the plural) Any prayer spoken inaudibly and not aloud; especially, one of the prayers in the Tridentine Mass, immediately following the "orate, fratres", said inaudibly by the celebrant.

(transitive) To make or keep secret.

(transitive) To hide secretly.

Being or kept hidden.