The first occurrence.
And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day. Gen 1:5
The primitive root.
Strong’s H3117, yom, a concrete noun meaning “day;” from an unused root meaning, “to be hot.” The 3-letter root of the noun is yud + vav + mem.
yud י = the closed hand, thus work, throw, worship
vav ו = the tent peg, thus add, secure, hook
mem מ, ם = the water, thus chaos, mighty, blood
The story: The work (yud) to secure or bring order (vav) to chaos (mem) is done during the daylight hours.