lefthander vs left-hander

lefthander and left-hander both are nouns.

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

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

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

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

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