cavalryman vs lancer

cavalryman and lancer both are nouns.

Word	Noun	Adjective	Verb	Adverb
cavalryman	Yes	No	No	No
lancer	Yes	No	No	No

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

Other hyponyms of cavalryman include cuirassier, dragoon, hussar, Rough Rider.

cavalryman (noun)	lancer (noun)
a soldier mounted on horseback	(formerly) a cavalryman armed with a lance
a soldier in a motorized army unit