Jolie

When a brother and sister have a very close relationship that more resembles that of a boyfriend and girlfriend, they are said to be jolie.

The term originates from the risqué relationship between Angelina Jolie and her brother James Haven, who have been known to share passionate kisses in public.

Pronounced more like jolly.

"That brother and sister were little too jolie for my liking. Siblings shouldn't use tongues."