An oarswoman is a woman who rows a boat, especially in races. It was made to stand beside oarsman, so that a female racer had a matching word. The work is the same: sit in the boat, pull the oar, keep time. Though actually, in ordinary talk, rower is the word you will hear most, for anyone. Oarswoman turns up in sports reports, club history, and when a writer wants to mark that the crew is female. The plural is oarswomen. It is not a different sport from rowing, and it does not mean a woman who sells or mends oars.