The Collaborative International Dictionary of English v.0.48:

Trousers \Trou"sers\, n. pl. [OF. trousses breeches worn by
   pages, from trousse, trosse, a bundle, a truss. See Truss,
   and cf. Trossers, Trouse.]
   A garment worn by men and boys, extending from the waist to
   the knee or to the ankle, and covering each leg separately.
   [1913 Webster]