herdsman vs goat herder

herdsman and goat herder both are nouns.

Word	Noun	Adjective	Verb	Adverb
herdsman	Yes	No	No	No
goat herder	Yes	No	No	No

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

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

herdsman (noun)	goat herder (noun)
someone who drives a herd	a person who tends a flock of goats