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When you have that extra bit hanging over your belt....another word for muffin top.
Marie: I like them jeans on her.

Emma: eww no look at the spare tyre hanging over the top in all its mushy greatness.

Marie: yeah you're right they'd look so much better on me hohoho!
by The Hippy Hippy shake October 25, 2007
the definition of spare tyre - when the female or male uses the female or male when either are feeling down. ( for example, when the tyres flat on a vehicle, you only use it when you need to ).

or - the person uses one another when he or she only needs or wants something
she's treating me like a spare tyre
by eshay1na March 30, 2011