(idiomatic, as response or with indirect question) I don't know; I have no idea.

The delivery point where Mail Services delivers and collects mail.

(idiomatic) I received the information from a source not to be overtly exposed.

Alternative form of man of action

(anatomy) The tough and inflexible outermost of the three layers of the meninges, enveloping the brain and spinal cord.

A tree of the genus Acer, characterised by its usually palmate leaves and winged seeds. / The wood of such a tree, prized for its hardness and attractive appearance

(US, Canada, education) To take (something) as one's major field of study in an institute of tertiary education (such as a college or university).

(idiomatic) Everything; the entire collection, endeavor, or activity.

(idiomatic) I don't understand any of it; it makes no sense.

Believe me; rest assured.