Twinsome 

The action of having sex with twins, much like a threesome.

I want to have a twinsome with Jack and Finn Harries

Twinsome by parisssssssss October 23, 2012

twinsome 

Like a Threesome, but with twins and one other partner.

Look at those 2 twin blondes playing pool, think I'm gonna get me a twinsome.

twinsome by Jeff Delaney July 8, 2005

Twinometry 

in a homosexual relationship, there is almost always a "boy" and a "girl". The "boy" is simply the dominant of the two regardless of gender while the "girl" is the submissive. sometimes, there is neither a boy or a girl, and the two are as equals in dominance as identical twins would share equal behaviors recieved by the parents and actions towards each other. In short, a twinometric relationship, the partners are seen as equals instead of having a dominance complex.

Dan: "So, I heard you got yourself a boyfriend... who's on top?"
Tom: "We take turns each night, if you must know. It's a perfect twinometry.

Twinometry by guyswholikeguyswholikeguys September 13, 2009

twincome 

When one twin makes money for both twins.

Twin A: Hey did you get paid today?
Twin B: F**K YEAH I did! Let's go to Steak & Shake
Twin A: Yay for twincome!
Spectator: (confused but envious)

twincome by realtwinzz October 23, 2009