The Collaborative International Dictionary of English v.0.48:

Lucite \Lu"cite\ (l[=oo]"s[imac]t), prop. n.
   A brand name for a transparent plastic based on methyl
   methacrylate esters; the term is often used generically to
   refer to any similar transparent plastic. It is sold in
   various forms, including rigid sheets which may be used as a
   substitute for glass in windows. [Trademark]
   [PJC]

WordNet (r) 3.0 (2006):

Lucite
    n 1: a transparent thermoplastic acrylic resin [syn: Lucite,
         Perspex]