backup man vs locum

backup man and locum both are nouns.

Word	Noun	Adjective	Verb	Adverb
backup man	Yes	No	No	No
locum	Yes	No	No	No

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

backup man: someone who takes the place of another (as when things get dangerous or difficult)
locum: someone (physician or clergyman) who substitutes temporarily for another member of the same profession

Other hyponyms of backup man include locum tenens, double, alternate, replacement, surrogate.

backup man (noun)	locum (noun)
someone who takes the place of another (as when things get dangerous or difficult)	someone (physician or clergyman) who substitutes temporarily for another member of the same profession