Webster's Revised Unabridged Dictionary · 1913

Décolleté

Décolleté (da`kol`le*ta") , adjective

[French, past participle of décolleter to bare the neck and shoulders; dé- + collet collar, from Latin collum neck.]

1.
Leaving the neck and shoulders uncovered; cut low in the neck, or low-necked, as a dress.
2.
Wearing a décolleté gown.

Also: Decollete