pitcher vs lefthander

pitcher and lefthander both are nouns.

Word	Noun	Adjective	Verb	Adverb
pitcher	Yes	No	No	No
lefthander	Yes	No	No	No

As nouns, lefthander is a hyponym of pitcher; that is, lefthander is a word with a more specific, narrower meaning than pitcher:

pitcher (noun)	lefthander (noun)
the position on a baseball team of the player who throws the ball for a batter to try to hit	a baseball pitcher who throws the ball with the left hand
an open vessel with a handle and a spout for pouring
(baseball) the person who does the pitching
(botany) a leaf that is modified in such a way as to resemble a pitcher or ewer
the quantity contained in a pitcher