herdsman vs sheepherder

herdsman and sheepherder both are nouns.

Word	Noun	Adjective	Verb	Adverb
herdsman	Yes	No	No	No
sheepherder	Yes	No	No	No

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

herdsman: someone who drives a herd
sheepherder: a herder of sheep (on an open range); someone who keeps the sheep together in a flock

Other hyponyms of herdsman include goat herder, goatherd, sheepman, shepherd, pigman, swineherd.

herdsman (noun)	sheepherder (noun)
someone who drives a herd	a herder of sheep (on an open range); someone who keeps the sheep together in a flock