A lavalier or lavaliere or lavalliere is an item of jewelry consisting of a pendant, sometimes with one stone, suspended from a necklace.
The style was popularized by the Duchesse de la Vallière, a mistress of King Louis XIV of France. A lavalier can be recognized most for its drop (that usually consist of a stone and/or a chandelier type of drop) which is attached to the chain and not attached by a bail.
According to Hans Nadelhoffer, Cartier: Jewelers Extraordinary (1984), p. 50:
A special form of necklace produced around 1900 was the lavallière, an imaginative allusion to a fashion named for the actress Ève Lavallière, suspending two overlapping pendants, generally of different lengths. The necklace itself often consisted of a simple silk cord with diamond sliding motifs, in which the imaginative end motifs were often intertwined. Princess George of Greece (Marie Bonaparte) received a lavallière with two diamond fir cones, the Tsarina of Russia one with amethyst acorns. Eve Lavallière made her debut in 1891 at the Théâtre des Variétés, having previously worked in a hat factory, tying ribbons. The cravats which were produced in this way were called lavallières and provided a stage-name for the actress, whose real name was Eve Ferroglio. She died in a convent in 1929.
"Lavallière" is still the French name for an ascot tie.
Later, the American collegiate fraternity system ("Greeks") adopted a lavalier which contained the fraternity letters as part of or within the pendant to symbolize involvement in an ongoing romantic relationship which may become a long-term relationship resulting in becoming "pinned" (woman receiving the man's fraternity pin to wear), engaged and married.