A key part of a ship’s steering apparatus. Ancient sailing vessels had various styles and numbers of rudders. Some had a single  steering oar. Usually, however, Greek and Roman ships had two steering paddles at the stern, each probably capable of being operated independently through a rowlock (something like an open porthole). When the vessel was anchored, the rudder oars were held out of the water by lashings or rudder bands.

“Rudder oars” (“steering-paddles,” NE) were used to guide the vessel on which Paul was sailing en route to Rome and which was wrecked on Malta. The anchors were cut away, and before the foresail was hoisted, the lashings were loosened, freeing the rudder oars to aid the sailors in directing the ship toward the beach.​—Ac 27:40.

James (3:4, 5) shows the tremendous power the tongue has in controlling the direction of one’s whole body by comparing it to the relatively small rudder (“rudder-oar,” Int) of a large ship.