When it looks like you have one massive breast. This usally happens when a girl wears a sports bra or one of those tank tops with the shelf bra.

One who has a mania for music.

Condition when a woman wears a tight lycra fitted tube top for exercising and looses form of two boobs to just one

When a woman's bra isn't very supportive and doesn't separate, squeezing the boobs together, thus forming the appearance of one large boob. This usually happens with sports bras.

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. Therefore causing the appearance of "One Boob".

an amorphous undelineated mass of tit, often caused by old age sagginess or bras that squish them together. in theory, it could be a single cycloptic tit.

One boob that extends the same distance as if you had 2 boobs. its quite unfortunate and can often happen when so much fat has extended across the barrier from one breast to the other, forming a uni boob.