weight gainer vs gainer

weight gainer and gainer both are nouns.

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

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

weight gainer (noun)	gainer (noun)
a person who gains weight	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 (gains an advantage or gains profits)
	a person who gains weight