uniboob. When a larger chested woman wears a sports bra it is tremendously restricting. It is described as -- A large lump of two breasts squeezed together by the wearing of a sports bra.The end result is that the woman's breasts no longer have the Lift and Separate affect. should get me one of those. by lizzie millard November 08, 2007. 5. uniboob. A case of the rare condition called symmastia, in which a woman's two breasts literally grow together and join in the middle of the chest, so it looks like a single dumbell-shaped breast across the chest.