yardmaster vs railwayman

yardmaster and railwayman both are nouns.

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

As nouns, railwayman is a hypernym of yardmaster; that is, railwayman is a word with a broader meaning than yardmaster:

Other hypernyms of yardmaster include dispatcher, railroad man, railroader, railway man, trainman.

yardmaster (noun)	railwayman (noun)
a railroad employer who is in charge of a railway yard	an employee of a railroad