Where does “excusen” come from?

excusen (Middle English) comes from Old French escuser, from Latin excūsō, from Latin causa, from Old Latin caussa, from Proto-Indo-European kawd-teh₂.

Ancestry of “excusen”, step by step

Step	Language	Word	Meaning
1	Old French	escuser	to excuse oneself; to make excuses
2	Latin	excūsō	to excuse, allege in excuse, free from a charge
3	Latin	causa	cause, reason; case, claim, contention; motive,...
4	Old Latin	caussa	cause, reason, purpose; case, claim; Archaic form...
5	Proto-Indo-European	kawd-teh₂	—

Every word from Proto-Indo-European kawd-teh₂ →Every word from Old Latin caussa →Every word from Latin causa →