limit vs keep down

limit is a noun but keep down is not a noun.

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

As verbs, keep down is a hyponym of limit; that is, keep down is a word with a more specific, narrower meaning than limit:

Other hyponyms of limit include hold down, number, cap, curb, curtail, cut back, restrict.

limit (noun)	keep down (noun)
the greatest possible degree of something
the boundary of a specific area
as far as something can go
the greatest amount of something that is possible or allowed
the mathematical value toward which a function goes as the independent variable approaches infinity
final or latest limiting point

limit (verb)	keep down (verb)
restrict or confine within limits	manage not to throw up
place limits on (extent or amount or access)	place a limit on the number of
decide upon or fix definitely	put down by force or intimidation