append vs affix

append is not a noun while affix is a noun.

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

As verbs, append and affix are synonyms defined as:

Other synonyms of append include add on, supplement.

append (noun)	affix (noun)
	a linguistic element added to a word to produce an inflected or derived form

append (verb)	affix (verb)
state or say further	stick or fasten to
fix to; attach	add to the very end
add to the very end	attach or become attached to a stem word