A sibling, most often either a step-sibling or close friend who is considered a sibling, to whom one is sexually attracted. In almost all cases, one has no aversion whatsoever to acting upon this attraction.
Isn't that his sister he's making out with over there? - Nah, they're just sinblings. His mom married her dad.
by Skippitynicsnushcicle September 21, 2010