left-hander vs left hander

left-hander and left hander both are nouns.

Word	Noun	Adjective	Verb	Adverb
left-hander	Yes	No	No	No
left hander	Yes	No	No	No

As nouns, left-hander and left hander are synonyms defined as:

left-hander and left hander: a baseball pitcher who throws the ball with the left hand

Other synonyms of left-hander include left-handed pitcher, lefthander, lefty, southpaw.

left-hander (noun)	left hander (noun)
a person who uses the left hand with greater skill than the right	a baseball pitcher who throws the ball with the left hand
a baseball pitcher who throws the ball with the left hand