polymethyl methacrylate

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry A thermoplastic transparent plastic manufactured by the polymerization of methyl methacrylate, often used in place of glass - it being lighter, softer and not shattering on impact.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a transparent plastic used as a substitute for glass