What is the meaning of Nock?

Either of the two grooves in a bow that hold the bowstring.

The notch at the rear of an arrow that fits on the bowstring.

The upper fore corner of a boom sail or trysail.

To fit (an arrow) against the bowstring of a bow or crossbow.

To cut a nock in (usually in an arrow's base or the tips of a bow).

fit the arrow to your bowstring

Misspelling of knock.

ridge (of a roof)

tappet

nock

end (of a yard, arm, boom, or gaff)

Source: wiktionary.org