buffet vs knock about

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

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

As verbs, buffet and knock about are synonyms defined as:

Other synonyms of buffet include batter.

buffet (noun)	knock about (noun)
a piece of furniture that stands at the side of a dining room; has shelves and drawers
usually inexpensive bar
a meal set out on a buffet at which guests help themselves

buffet (verb)	knock about (verb)
strike against forcefully	strike against forcefully
strike, beat repeatedly	be around; be alive or active