Something not understood or known.
Private seclusion.
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.
A form of steel skullcap.
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.
To make or keep secret.
To hide secretly.
Being or kept hidden.
Used other than figuratively or idiomatically: see unknown, quantity.
A person or thing whose nature or value is a mystery.