noun
watchmaker; clockmaker
A professional who makes, repairs, or designs watches and clocks. The term is neutral and can refer to both modern and traditional horologists.
彼はスイスで修行した時計師です。
He is a watchmaker who trained in Switzerland.
この古い柱時計は、腕のいい時計師に修理してもらった。
I had this old wall clock repaired by a skilled clockmaker.
時計屋 is a more casual term for a watch shop or watch seller, while 時計師 specifically refers to a skilled craftsman or horologist.
Compound of 時計 (clock/watch) and 師 (master, expert). The spelling 時計士 uses 士 (professional) with a similar meaning.