look up any word, like donkey punch:
Noun: A pretty girl. She's kind, sweet and just a little bit hyper. A Rhainnon will make anybody laugh and think all at the same time. A real swell gal.
"I got stuck the other day and a stranger stopped to help me."

"Wow, must have been a Rhainnon."
by BatmanSpiderman August 16, 2011