1. An implement for impelling a boat, being a slender piece of timber, usually ash or spruce, with a grip or handle at one end and a broad blade at the other. The part which rests in the rowlock is called the loom.
An oar is a kind of long paddle, which swings about a kind of fulcrum, called a rowlock, fixed to the side of the boat.
2. An oarsman; a rower; as, he is a good car.
3. (Science: zoology) An oarlike swimming organ of various invertebrates. Oar cock (Zool), the water rail. Spoon oar, an oar having the blade so curved as to afford a better hold upon the water in rowing. To boat the oars, to cease rowing, and lay the oars in the boat. To feather the oars. See Feather, To lie on the oars, to cease pulling, raising the oars out of water, but not boating them; to cease from work of any kind; to be idle; to rest. To muffle the oars, to put something round that part which rests in the rowlock, to prevent noise in rowing. To put in one’s oar, to give aid or advice; commonly used of a person who obtrudes aid or counsel not invited. To ship the oars, to place them in the rowlocks. To toss the oars, To peak the oars, to lift them from the rowlocks and hold them perpendicularly, the handle resting on the bottom of the boat. To trail oars, to allow them to trail in the water alongside of the boat. To unship the oars, to take them out of the rowlocks.
Origin: AS. Ar; akin to Icel. Ar, Dan. Aare, Sw. Ara; perh. Akin to E. Row, v. Cf. Rowlock.
Source: Websters Dictio