timepiece vs timer

timepiece and timer both are nouns.

Word	Noun	Adjective	Verb	Adverb
timepiece	Yes	No	No	No
timer	Yes	No	No	No

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

Other hyponyms of timepiece include atomic clock, clock, sandglass, sundial, ticker, watch.

timepiece (noun)	timer (noun)
a measuring instrument or device for keeping time	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