timekeeper vs timer

timekeeper and timer both are nouns.

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

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

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

As nouns, timekeeper and timer are synonyms defined as:

timekeeper and timer: (sports) an official who keeps track of the time elapsed

timekeeper (noun)	timer (noun)
a measuring instrument or device for keeping time	a timepiece that measures a time interval and signals its end
a clerk who keeps track of the hours worked by employees	a regulator that activates or deactivates a mechanism at set times
(sports) an official who keeps track of the time elapsed	(sports) an official who keeps track of the time elapsed