look up any word, like cunt:
 
3.
Friend with benefits.
Sophie: Are you and Brian officially a couple?
Nadia: No, we just hook up occasionally. He's my insignificant other.
by Flanhoodles April 16, 2008
 
1.
Someone you are casually dating, while seeing others on the side. This person is almost always someone you would never consider dating exclusively, but, you keep around as a backup plan for free Saturday nights.
Maria: Oo, the new guy in Calculus is cute!

Virginia: Wait, I thought you and James were dating?

Maria: No, no, we're just insignificant others.
by Madelaine June 13, 2006
 
2.
a phrase used to describe the cunt or douche that you used to officially have a relationship with that is still part of your life for whatever stupid reason that you're coming up with.
I took my (in)significant other to lunch yesterday. Not five minutes had passed before she was correcting my grammar and telling me that I was eating with the wrong fork. I LIKE THE LITTLE FORK.
by Milowe October 21, 2010
 
4.
Someone you are casually dating, while seeing others on the side. This person is almost always someone you would never consider dating exclusively, but, you keep around as a backup plan for free Saturday nights.
Maria: Oo, the new guy in Calculus is cute!

Virginia: Wait, I thought you and James were dating?

Maria: No, no, we're just insignificant others.
by Madelaine July 11, 2006