add on vs add

add on and add both are verbs.

Word	Noun	Adjective	Verb	Adverb
add on	No	No	Yes	No
add	No	No	Yes	No

As verbs, add is a hypernym of add on; that is, add is a word with a broader meaning than add on:

add on: make an addition
add: make an addition (to); join or combine or unite with others; increase the quality, quantity, size or scope of

add on (verb)	add (verb)
make an addition	make an addition (to); join or combine or unite with others; increase the quality, quantity, size or scope of
add to the very end	make an addition by combining numbers
	determine the sum of
	state or say further
	bestow a quality on
	constitute an addition