Where does “cwmwl” come from?

cwmwl (Middle Welsh) comes from Proto-Brythonic kuml, from Latin cumulus, from Proto-Indo-European ku-m-olo, from Proto-Indo-European ḱewh₁- — to swell; to be strong.

Ancestry of “cwmwl”, step by step

Step	Language	Word	Meaning
1	Proto-Brythonic	kuml	cloud
2	Latin	cumulus	heap, pile; surplus; summit
3	Proto-Indo-European	ku-m-olo	—
4	Proto-Indo-European	ḱewh₁-	to swell; to be strong

Words derived from “cwmwl”

cwmwl
cymylu

Every word from Proto-Indo-European ḱewh₁- →Every word from Proto-Indo-European ku-m-olo →Every word from Latin cumulus →