stop watch vs timer

stop watch and timer both are nouns.

Word	Noun	Adjective	Verb	Adverb
stop watch	Yes	No	No	No
timer	Yes	No	No	No

As nouns, timer is a hypernym of stop watch; that is, timer is a word with a broader meaning than stop watch:

stop watch: a timepiece that can be started or stopped for exact timing (as of a race)
timer: a timepiece that measures a time interval and signals its end

stop watch (noun)	timer (noun)
a timepiece that can be started or stopped for exact timing (as of a race)	a timepiece that measures a time interval and signals its end
	a regulator that activates or deactivates a mechanism at set times
	(sports) an official who keeps track of the time elapsed