noun A type of lever used to propel a boat, having a flat blade at one end and a handle at the other, and pivoted in a rowlock atop the gunwale, whereby a rower seated in the boat and pulling the handle can pass the blade through the water by repeated strokes against the water's resistance, thus moving the boat.
noun An oarsman; a rower.
He is a good oar.
noun An oar-like swimming organ of various invertebrates.