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1.
noun. Someone who has something in common with someone else.
Oh, you failed that test too? Twinsies!
by Comic March 18, 2005
 
2.
When you and someone else have something in common.
When you see someone wearing the same boots as you, "TWINSIES"
by BONQUISHA Charice October 18, 2012
 
3.
Plural form of Twinsie: Pictures taken of oneself and another person.

Both persons will be mirroring each other's acts, poses, silliness, or facial expressions as if twins. One of the two will be usually holding the camera with your arms stretched out to take the picture (part of arm stretched out can usually be seen in pictures taken). At rare occasions, twinsies may be taken using a tripod or through the help of a passer-by.
"Hey, have you seen Kaung's new profile picture on Facebook? He took off his Selfie and uploaded a Twinsie with his girl."
"Oh really? I didn't notice that. Most couples are doing Twinsies these days!"
"Ya, not just couples, I saw friends doing that too now."
by TheKMK November 21, 2013
 
4.
best friends (usually a boy and girl) who are almost identical in every way but aren't actually related so if one should want to be with the other or they hook up, it isn't weird
omg we're like twins" "but we dated and you like me..." "so we're twinsies!
by prince1993 October 17, 2010