Typically the willy found on a horse.

Also an exclamation or silence-filler. This is usually accidental. A form of tourettes.
"So that's a big pile of Horse Willy then..."

"Horse Willy. So..when shall we go shopping?"

"I'm scared! Horse Willy. I don't want to see to terrible people at university today."
by terribleterriblefabulous January 15, 2007
Get the Horse Willy mug.