1.  cotillion(n = noun.event) cotilion - a ball at which young ladies are presented to society;
is a kind of ball, formal

2.  cotillion(n = noun.act) cotilion - a lively dance originating in France in the 18th century;
is a kind of ballroom dance, ballroom dancing

1.  A brisk dance, performed by eight persons; a quadrille. [1913 Webster]

2.  A tune which regulates the dance. [1913 Webster]

3.  A kind of woolen material for women's skirts.

4.  A formal ball, especially one at which debutantes are first presented to society. [1913 Webster]

cotillion, n.
1 any of various French dances with elaborate steps, figures, and ceremonial.
2 US a a ballroom dance resembling a quadrille. b a formal ball.

Etymology:
F cotillon petticoat, dimin. of cotte f. OF cote COAT