πηδάλιον, -συ, τό (< πηδός, the blade of an oar), a rudder: Jas.3:4; pl., Act.27:40.† (AS)
Thayer:
1) a ship's rudder
πηδάλιον
pēdalion
pay-dal'-ee-on
Neuter of a (presumed) derivative of πηδόν pēdon (the blade of an oar; from the same as G3976); a “pedal”, that is, helm