Knock \Knock\, n.

1. A blow; a stroke with something hard or heavy; a jar.

2. A stroke, as on a door for admittance; a rap. `` A knock at the door.'' --Longfellow.

A loud cry or some great knock. --Holland.

Knock off, a device in a knitting machine to remove loops from the needles.

Source: Webster's Revised Unabridged Dictionary (1913)