railwayman vs signalman

railwayman and signalman both are nouns.

Word	Noun	Adjective	Verb	Adverb
railwayman	Yes	No	No	No
signalman	Yes	No	No	No

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

railwayman: an employee of a railroad
signalman: a railroad employee in charge of signals and point in a railroad yard

Other hyponyms of railwayman include brakeman, yardman, train dispatcher, trainmaster, yardmaster.

railwayman (noun)	signalman (noun)
an employee of a railroad	a railroad employee in charge of signals and point in a railroad yard