postfix vs termination

postfix and termination both are nouns.

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

As nouns, termination is a hypernym of postfix; that is, termination is a word with a broader meaning than postfix:

postfix: an affix that is added at the end of the word
termination: the end of a word (a suffix or inflectional ending or final morpheme)

Other hypernyms of postfix include affix, ending.

postfix (noun)	termination (noun)
an affix that is added at the end of the word	the act of ending something
	the end of a word (a suffix or inflectional ending or final morpheme)
	something that results
	a place where something ends or is complete
	a coming to an end of a contract period