return ticket vs round-trip ticket

return ticket and round-trip ticket both are nouns.

Word	Noun	Adjective	Verb	Adverb
return ticket	Yes	No	No	No
round-trip ticket	Yes	No	No	No

As nouns, return ticket and round-trip ticket are synonyms defined as:

return ticket and round-trip ticket: a ticket to a place and back (usually over the same route)

return ticket (noun)	round-trip ticket (noun)
a ticket to a place and back (usually over the same route)	a ticket to a place and back (usually over the same route)