Where does “pitter” come from?

pitter (Middle High German) comes from Old High German bittar, from Old Norse bitr, from Proto-Germanic bitraz, from Proto-Indo-European bʰidrós — biting, splitting.

Ancestry of “pitter”, step by step

Step	Language	Word	Meaning
1	Old High German	bittar	bitter
2	Old Norse	bitr	bitter
3	Proto-Germanic	bitraz	bitter
4	Proto-Indo-European	bʰidrós	biting, splitting

Every word from Proto-Indo-European bʰidrós →Every word from Proto-Germanic bitraz →Every word from Old Norse bitr →