watcher vs fire watcher

watcher and fire watcher both are nouns.

Word	Noun	Adjective	Verb	Adverb
watcher	Yes	No	No	No
fire watcher	Yes	No	No	No

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

watcher: a guard who keeps watch
fire watcher: (during World War II in Britain) someone whose duty was to watch for fires caused by bombs dropped from the air

watcher (noun)	fire watcher (noun)
a guard who keeps watch	(during World War II in Britain) someone whose duty was to watch for fires caused by bombs dropped from the air
a close observer; someone who looks at something (such as an exhibition of some kind)
a person who keeps a devotional vigil by a sick bed or by a dead body