tighten one's belt vs save

tighten one's belt is not a noun while save is a noun.

Word	Noun	Adjective	Verb	Adverb
tighten one's belt	No	No	Yes	No
save	Yes	No	Yes	No

As verbs, save is a hypernym of tighten one's belt; that is, save is a word with a broader meaning than tighten one's belt:

Other hypernyms of tighten one's belt include economise, economize.

tighten one's belt (noun)	save (noun)
	(sports) the act of preventing the opposition from scoring

tighten one's belt (verb)	save (verb)
live frugally and use less resources	make unnecessary an expenditure or effort
	record data on a computer
	to keep up and reserve for personal or special use
	accumulate money for future use
	spend less; buy at a reduced price
	retain rights to
	spend sparingly, avoid the waste of
	bring into safety
	save from ruin, destruction, or harm
	save from sins
	refrain from harming