co·til·lion also co·til·lon 
(kō-tĭlyən, kə-)
(kō-tĭlyən, kə-)n.
1. A formal ball, especially one at which young women are presented to society.
2.
a. A lively dance, originating in France in the 18th century, having varied, intricate patterns and steps.
b. A quadrille.
c. The music for these dances.
[French cotillon, from Old French, petticoat, diminutive of cote, coat; see COAT.]