The Collaborative International Dictionary of English v.0.48:

macromolecule \mac`ro*mol"e*cule\, n. (Chem., Biochem.)
   A very large molecule, especially a polymer having from
   hundreds to many thousands of atoms, such as DNA, RNA,
   protein, polysaccharide, polyethylene, polycarbonate,
   etc.
   [PJC]

WordNet (r) 3.0 (2006):

polyethylene
    n 1: a lightweight thermoplastic; used especially in packaging
         and insulation [syn: polyethylene, polythene]