1. To strike loudly and sharply or to draw attention to a situation or circumstance: Dina will knock loudly on the door so the residents will know that they have visitors.
2. To criticize or to find fault: Because Mark felt insecure, he was always trying to knock his colleagues about their work.

A loud pounding noise: The engine in Trudy's car has developed an awful knock and so she must take it to the garage.

1. The groove at either end of a bow for holding the bowstring: The huntsman strung his bow, placing the bowstring in the nock at each end of the bow.
2. The notch in the end of an arrow that fits on the bowstring: Rosario fit the nock of the new arrow carefully onto the bowstring before aiming her shot.