sistoid 

Your sister from your immediate family.

My sistoid is coming home after she eats at Tony's Pizzas.

sistoid by R Woods December 23, 2006

Sistoitis

A seemingly never-ending virus usually contracted in Las Vegas from a Charlestown sickling

DUNNY: Man, I was dunnygaming last night and I don't feel so good today. I thought that's what it was anyway...
SASSTO: Well, what was it?
DUNNY: I caught the Sistoitis.
SASSTO: Oh man! Sorry!
FLEER FLAWN: Yitadee!

Sistoitis by Kirtan February 20, 2009