knock vs knock about

knock is a noun but knock about is not a noun.

Word	Noun	Adjective	Verb	Adverb
knock	Yes	No	Yes	No
knock about	No	No	Yes	No

knock (noun)	knock about (noun)
the act of hitting vigorously
negative criticism
a vigorous blow
the sound of knocking (as on a door or in an engine or bearing)
a bad experience

knock (verb)	knock about (verb)
find fault with; express criticism of; point out real or perceived flaws	strike against forcefully
knock against with force or violence	be around; be alive or active
rap with the knuckles
deliver a sharp blow or push
make light, repeated taps on a surface
sound like a car engine that is firing too early