ex-twin 

1) girls who became friends and then learned they have the same ex

2) girls who became friends after breaking up with a guy cheating on them

3) girls who both hate their ex (they have the same ex obviously) and bonded over that

"ally is my ex-twin and my bestie!"

ex-twin by thesneeky1 May 21, 2016

Third twin

The backup twin

"You must be the third twin of the family"

Third twin by MShadow2016 August 12, 2016

opposite twin 

My mf nigga that been by my side since day 1

That's my opposite twin forever

opposite twin by Tiva.marcy March 16, 2017

Forever Twin 

When 2 people have the same birthday and have similar personalities and are best friends forever and help each other all the time is a true bond between them

My twin Autumn is the best ever she helps me I help her and I hope we never get separated from each other because what we have is unbelievable strong and so unique it’s never gunna be the same

Autumn and I were meant to be together for the rest of our lives we’re Forever Twins

Forever Twin by Boyer Amber April 9, 2018

chin twin 

When two people have chins that look identical

That baby has the same awesome chin as her cool aunt, they are chin twins!

chin twin by Cool Aunt June 12, 2018

Better twin 

Popular person, the cool one, which only hangs out with people like itself.

-"Peter has never spoken to us since first grade."
-"Why are you so astonished, he's ultimately a better twin."

Better twin by Misiaczek February 28, 2019

number twin 

Someone who has the same phone number you have except for the for the area code. [phone] and [phone]

I met this person last night and when she gave me her phone number it was the same as mine except for the city area code. We are like number twins or something!

number twin by Cot Crunch August 6, 2019