cowherd vs cowboy

cowherd and cowboy both are nouns.

Word	Noun	Adjective	Verb	Adverb
cowherd	Yes	No	No	No
cowboy	Yes	No	No	No

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

cowherd: a hired hand who tends cattle and performs other duties on horseback
cowboy: a male hired hand who tends cattle and performs other duties on horseback

Other hyponyms of cowherd include buckaroo, buckeroo, vaquero, cowgirl, gaucho, horse wrangler, wrangler, roper, cattleman, cowman.

cowherd (noun)	cowboy (noun)
a hired hand who tends cattle and performs other duties on horseback	someone who is reckless or irresponsible (especially in driving vehicles)
	a performer who gives exhibitions of riding and roping and bulldogging
	a male hired hand who tends cattle and performs other duties on horseback