press-up vs pushup

press-up and pushup both are nouns.

Word	Noun	Adjective	Verb	Adverb
press-up	Yes	No	No	No
pushup	Yes	No	No	No

As nouns, press-up and pushup are synonyms defined as:

press-up and pushup: an arm exercise performed lying face to the floor and pushing the body up and down with the arms

press-up (noun)	pushup (noun)
an arm exercise performed lying face to the floor and pushing the body up and down with the arms	an arm exercise performed lying face to the floor and pushing the body up and down with the arms