Where does “Clancy” come from?

Clancy (English) comes from Irish Mac Fhlannchaidh, from Irish Flann, from Middle Irish flann, from Proto-Celtic wlannos, from Proto-Indo-European welh₃- — to hit, to strike.

Ancestry of “Clancy”, step by step

Step	Language	Word	Meaning
1	Irish	Mac Fhlannchaidh	—
2	Irish	Flann	—
3	Middle Irish	flann	blood-red, crimson; blood
4	Proto-Celtic	wlannos	—
5	Proto-Indo-European	welh₃-	to hit, to strike

Every word from Proto-Indo-European welh₃- →

Clancy — Etymology, Origin & Word History | Etymology Explorer