%decolletage%

‖n. [ F. See Décolleté. ] (Costume) 1. The upper border or part of a low-cut (i.e., décolleté) dress. [ Webster 1913 Suppl. +PJC ]

2. The exposed upper parts of the breasts of a woman wearing a low-cut dress; as, transfixed by her stunning decolletage. [ PJC ]