Middle English word rydder comes from Proto-Italic *krinō (Decide. Distinguish, discern. Sift, separate.)

Detailed word origin of rydder

Dictionary entry	Language	Definition
*krinō	Proto-Italic (itc-pro)	Decide. Distinguish, discern. Sift, separate.
*krey-	Proto-Indo-European (ine-pro)
cernere	Latin (lat)
*hrid-	Proto-Germanic (gem-pro)
*hrīdrǭ	Proto-Germanic (gem-pro)	Sieve.
hrīder	Old English (ang)
ridder	Middle English (enm)