The Collaborative International Dictionary of English v.0.48:

blue jeans \blue" jeans`\, n. pl.
   a tight-fitting trousers made of blue denim or a similar
   fabric, designed originally to serve as inexpensive durable
   workclothes, and often having metal rivets for reinforcement.
   They have become very popular as casual wear for all age
   groups, and more expensive and more carefully styled and
   tailored versions called designer jeanshave also become
   popular among girls and women.

   Syn: jeans, Levis. [1913 Webster]