Indeed, it is not a taboo subject anymore! In fact, I frequently read about it in news papers mentioning this as dressing sense or beauty of a woman (I guess there are competitions as well).
Whatever--a dressing sense--or naturally forming 'deep cut', some have it well-defined, others simply show its absence.
Now there could be two opposites in this case and I am searching for both those terms.
A) What's the opposite term for the word 'cleavage' - a woman with absence of cleavage (flat or no cleavage does not convince me).
B) What's the term that describes opposite of cleavage itself - cleavage is *the space between the organs that can be seen above a dress but then some dresses (not uploading a picture here to keep this site graphically clean) show them from the bottom i.e. below the top (opposite direction)? What's the term for that? Cleavage from Bottom? 'Bottom Cleft' - no way. No word with bottom (#7) can prevent ambiguity here.