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1.
When two people who are not related share literally almost everything in common, and are better than best friends with each other.
Mike and Katie arent related. They both hate socks and projects. But they both love orange starbursts and running.They also have everything else in common and always keep finding new things.This means they have a twinship.
by Maktie March 03, 2009
 
2.
having a best friend who could pass as your twin. not necessarily an identical twin, could be fraternal. finishing each others sentences, watching the same tv show at the same time, thinking the exact same thing, having interest in the same things, are all signs of twinship.
Anna: oh my god, i just figured out who sang that song on that commercial!
Molly: your kidding, i was just watching that and thinking about how i was gonna text you!
Anna: we are sooo twinsies! twinship!
by twinsiesssss123456 June 07, 2009