quash vs keep down

quash and keep down both are verbs.

Word	Noun	Adjective	Verb	Adverb
quash	No	No	Yes	No
keep down	No	No	Yes	No

As verbs, quash and keep down are synonyms defined as:

Other synonyms of quash include reduce, repress, subdue, subjugate.

quash (verb)	keep down (verb)
put down by force or intimidation	manage not to throw up
declare invalid	place a limit on the number of
	put down by force or intimidation