timer vs stop watch

timer and stop watch both are nouns.

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

As nouns, stop watch is a hyponym of timer; that is, stop watch is a word with a more specific, narrower meaning than timer:

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

Other hyponyms of timer include chronograph, parking meter, stopwatch.

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