Where does “grey” come from?

grey (Old Spanish) comes from Latin grex, from Proto-Indo-European ger- — to turn, bend, twist, wind; to tie, bind...

Ancestry of “grey”, step by step

Step	Language	Word	Meaning
1	Latin	grex	a group of smaller animals: a flock of birds, sheep, etc., a pack of dogs, wolves, etc., a swarm of insects, etc
2	Proto-Indo-European	ger-	to turn, bend, twist, wind; to tie, bind...