To strike with a hard blow. To affect in a specified way by striking hard: knocked the mugger senseless. To cause to collide: I knocked my head on a low beam. To produce by hitting or striking: knocked a hole in the wall. To instill with or as if with blows: We tried to knock some sense into his head. Slang To find fault with; criticize: Don't knock the food; it's free. To strike a sharp audible blow or series of blows, as on a door. To collide with something: knocked into the table. To make a pounding or clanking noise: The car engine is knocking. An instance of striking or colliding; a blow. The sound of a sharp tap on a hard surface; a rap. A pounding or clanking noise made by an engine, often as a result of faulty fuel combustion. Also called ping1. Slang A cutting, often petty criticism. around Informal To be rough or brutal with; maltreat. around Informal To wander from place to place: knocking around Europe. around Informal To discuss or consider: met to knock around some ideas. knock back Informal To gulp (an alcoholic drink). knock down To bring to the ground with a blow; topple. knock down To disassemble into parts, as for storage or shipping. knock down To declare sold at an auction, as by striking a blow with a gavel. knock down Informal To reduce, as in price: knocked each radio down 20 percent. knock down Slang To receive as wages; earn: knocks down $50 an hour. knock off To take a break or rest from; stop: knocked off work at noon. knock off To cease work: It's after five; let's knock off. knock off Informal To complete, accomplish, or dispose of hastily or easily; finish: That author knocks off a book a year.