stick on vs affix

stick on is not a noun while affix is a noun.

Word	Noun	Adjective	Verb	Adverb
stick on	No	No	Yes	No
affix	Yes	No	Yes	No

As verbs, stick on and affix are synonyms defined as:

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

stick on (verb)	affix (verb)
stick or fasten to	stick or fasten to
apply a heavy coat to	add to the very end
	attach or become attached to a stem word