cowherd vs vaquero

cowherd and vaquero both are nouns.

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

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

cowherd: a hired hand who tends cattle and performs other duties on horseback
vaquero: local names for a cowboy (`vaquero' is used especially in southwestern and central Texas and `buckaroo' is used especially in California)

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

cowherd (noun)	vaquero (noun)
a hired hand who tends cattle and performs other duties on horseback	local names for a cowboy (`vaquero' is used especially in southwestern and central Texas and `buckaroo' is used especially in California)