left-hander vs southpaw

left-hander and southpaw both are nouns.

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

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

left-hander and southpaw: a person who uses the left hand with greater skill than the right

Other synonyms of left-hander include lefty.

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

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

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

left-hander (noun)	southpaw (noun)
a person who uses the left hand with greater skill than the right	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