Where does “mud” come from?

mud (Middle English) comes from Middle Dutch modde, from Proto-Germanic mud-, from Proto-Indo-European mū- — fly, mosquito; fly, midge; lips, muzzle.

Ancestry of “mud”, step by step

Step	Language	Word	Meaning
1	Middle Dutch	modde	—
2	Proto-Germanic	mud-	—
3	Proto-Indo-European	mū-	fly, mosquito; fly, midge; lips, muzzle

mud — Etymology, Origin & Word History | Etymology Explorer