Where does “mejar” come from?

mejar (Old Portuguese) comes from Vulgar Latin meiare, from Latin meiō, from Proto-Italic meiɣjō, from Proto-Indo-European h₃meyǵʰ- — to urinate.

Ancestry of “mejar”, step by step

Step	Language	Word	Meaning
1	Vulgar Latin	meiare	—
2	Latin	meiō	—
3	Proto-Italic	meiɣjō	—
4	Proto-Indo-European	h₃meyǵʰ-	to urinate

mejar — Etymology, Origin & Word History | Etymology Explorer