level best vs limit

level best and limit both are nouns.

Word	Noun	Adjective	Verb	Adverb
level best	Yes	No	No	No
limit	Yes	No	Yes	No

As nouns, limit is a hypernym of level best; that is, limit is a word with a broader meaning than level best:

Other hypernyms of level best include bound, boundary.

level best (noun)	limit (noun)
the greatest possible degree	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

level best (verb)	limit (verb)
	restrict or confine within limits
	place limits on (extent or amount or access)
	decide upon or fix definitely