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1.
when one's bra is too small, and one or both boobs are poking over the top of the cup. there are varying degrees of overboob; and when a severe case affects both boobs, it is called quadriboob.
I haven't worn this bra in a while, I must've outgrown it... I've had overboob all day long and no one told me!
by the Cheshire Kat February 09, 2007
 
2.
Much like the "sideboob" the "Overboob" is the part of a woman's breast that is exposed or casually visible by others.
I think she needs a bigger bra. Look at all that "overboob" hangin' out.
by kyeat001 July 24, 2009