Hi, Bess, I know this thread's been silent for quite a while, but I couldn't help but respond a little bit to your inquiry with a bit of trivia I've picked up regarding Irish folklore and legend.
Finn McCool (Fionn mac Cumhail) had a son who was also a member of the Fianna and became the subject of a couple of different stories in the Fenian cycle of mythology, most particularly the story of "Tír na nOg" (should be a fada over the capital O - sorry), or "The Land of Eternal Youth". His name was "Oisín" (pronounced Oh-sheen) and means "fawn" or "little deer".
Fionn mac Cumhail was hunting one day when he spied a doe and was ready to shoot her with an arrow. His hounds, who had once been human, recognized that the doe was also human, so Fionn spared her and brought her to his land. She told him she had been cursed by a druid and turned into a deer because she would not marry him. Once she set foot on Fionn's land, she returned to her original form, and they married. But the druid returned and changed her back into a deer, so she fled. Later, Fionn met their son, Oisín, who, being the son of a woman turned into a deer, was named "fawn", even though it doesn't give it the ring of a great warrior, but makes sense in the context of the story.
Don't know if this helps you any, but I thought it was a fun tale of how his name came to be.
Dale D.