paste-up vs montage

paste-up and montage both are nouns.

Word	Noun	Adjective	Verb	Adverb
paste-up	Yes	No	No	No
montage	Yes	No	No	No

As nouns, montage is a hyponym of paste-up; that is, montage is a word with a more specific, narrower meaning than paste-up:

paste-up: a composition of flat objects pasted on a board or other backing
montage: a paste-up made by sticking together pieces of paper or photographs to form an artistic image

Other hyponyms of paste-up include collage.

paste-up (noun)	montage (noun)
a composition of flat objects pasted on a board or other backing	a paste-up made by sticking together pieces of paper or photographs to form an artistic image