sundial vs timepiece

sundial and timepiece both are nouns.

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

As nouns, timepiece is a hypernym of sundial; that is, timepiece is a word with a broader meaning than sundial:

sundial: timepiece that indicates the daylight hours by the shadow that the gnomon casts on a calibrated dial
timepiece: a measuring instrument or device for keeping time

Other hypernyms of sundial include horologe, timekeeper.

sundial (noun)	timepiece (noun)
timepiece that indicates the daylight hours by the shadow that the gnomon casts on a calibrated dial	a measuring instrument or device for keeping time