Source : Webster's Revised Unabridged Dictionary (1913)

D'ecolletage \D['e]`col`le*tage"\ (d[=a]`k[-o]`l'*t[.a]zh), n.
   [F. See {D['e]collet['e]}.] (Costume)
   The upper border or part of a d['e]collet['e] corsage.