buy into vs put

buy into is not a noun while put is a noun.

Word	Noun	Adjective	Verb	Adverb
buy into	No	No	Yes	No
put	Yes	No	Yes	No

As verbs, put is a hypernym of buy into; that is, put is a word with a broader meaning than buy into:

Other hypernyms of buy into include commit, invest, place.

buy into (noun)	put (noun)
	the option to sell a given stock (or stock index or commodity future) at a given price before a given date

buy into (verb)	put (verb)
buy stocks or shares of a company	arrange thoughts, ideas, temporal events
	estimate
	formulate in a particular style or language
	attribute or give
	put into a certain place or abstract location
	cause to be in a certain state; cause to be in a certain relation
	adapt
	cause (someone) to undergo something
	make an investment