rudder (n.)
Old English roðor "paddle, oar," from Proto-Germanic *rothru- (cognates: Old Frisian roðer, Middle Low German roder, Middle Dutch roeder, Dutch roer, Old High German ruodar, German Ruder "oar"), from *ro- "steer" (see row (v.)) + suffix -þra, used to form neutral names of tools. Meaning "broad, flat piece of wood attached to the stern of a boat and used for steering" is from c.1300. Spelling with -d- for -th- first recorded mid-15c. (compare feather (n.), mother (n.), gather).