gainer vs weight gainer

gainer and weight gainer both are nouns.

Word	Noun	Adjective	Verb	Adverb
gainer	Yes	No	No	No
weight gainer	Yes	No	No	No

As nouns, gainer and weight gainer are synonyms defined as:

gainer (noun)	weight gainer (noun)
a dive in which the diver throws the feet forward to complete a full backward somersault and enters the water feet first and facing away from the diving board	a person who gains weight
a person who gains (gains an advantage or gains profits)
a person who gains weight