1. To drink something, usually an alcoholic beverage, quickly. A noun or pronoun can be used between "knock" and "back." Let's get together and knock back some cold ones tonight.

2. To physically force someone or something backwards. A noun or pronoun can be used between "knock" and "back." The rumbling of the earthquake knocked us all back.

3. To cost someone a particular amount of money. A noun or pronoun can be used between "knock" and "back." Geez, how much is this car repair going to knock me back?