butt on vs butt against

butt on and butt against both are verbs.

Word	Noun	Adjective	Verb	Adverb
butt on	No	No	Yes	No
butt against	No	No	Yes	No

As verbs, butt on and butt against are synonyms defined as:

Other synonyms of butt on include abut, adjoin, border, butt, edge, march.

butt on (verb)	butt against (verb)
lie adjacent to another or share a boundary	lie adjacent to another or share a boundary
	collide violently with an obstacle