affix vs postfix

affix and postfix both are nouns.

Word	Noun	Adjective	Verb	Adverb
affix	Yes	No	Yes	No
postfix	Yes	No	No	No

As nouns, postfix is a hyponym of affix; that is, postfix is a word with a more specific, narrower meaning than affix:

affix: a linguistic element added to a word to produce an inflected or derived form
postfix: an affix that is added at the end of the word

Other hyponyms of affix include prefix, suffix, infix.

affix (noun)	postfix (noun)
a linguistic element added to a word to produce an inflected or derived form	an affix that is added at the end of the word

affix (verb)	postfix (verb)
stick or fasten to
add to the very end
attach or become attached to a stem word