1. （被车）撞倒
If someone is knocked down or is knocked over by a vehicle or its driver, they are hit by a car and fall to the ground, and are often injured or killed.

2. 推倒，拆掉，拆毁（建筑物）
To knock down a building or part of a building means to demolish it.

3. 降（价）；杀（价）；减（量）
To knock down a price or amount means to decrease it.

1. shatter as if by explosion

Synonym: blast

2. cause to come or go down

e.g. The policeman downed the heavily armed suspect
The mugger knocked down the old lady after she refused to hand over her wallet

Synonym: downcut downpush downpull down

3. knock down with force

e.g. He decked his opponent

Synonym: deckcoldcockdumpfloor