buy vs buy off

buy is a noun but buy off is not a noun.

Word	Noun	Adjective	Verb	Adverb
buy	Yes	No	Yes	No
buy off	No	No	Yes	No

As verbs, buy off is a hyponym of buy; that is, buy off is a word with a more specific, narrower meaning than buy:

Other hyponyms of buy include sop, pay off.

buy (noun)	buy off (noun)
an advantageous purchase

buy (verb)	buy off (verb)
accept as true	pay someone with influence in order to receive a favor
obtain by purchase; acquire by means of a financial transaction
make illegal payments to in exchange for favors or influence
acquire by trade or sacrifice or exchange
be worth or be capable of buying