railroad man vs yardman

railroad man and yardman both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad man	Yes	No	No	No
yardman	Yes	No	No	No

As nouns, yardman is a hyponym of railroad man; that is, yardman is a word with a more specific, narrower meaning than railroad man:

Other hyponyms of railroad man include brakeman, signalman, train dispatcher, trainmaster, yardmaster.

railroad man (noun)	yardman (noun)
an employee of a railroad	a laborer hired to do outdoor work (such as mowing lawns)
	worker in a railway yard