The Collaborative International Dictionary of English v.0.48:

Multilateral \Mul`ti*lat"er*al\, a. [Multi- + lateral.]
   Having many sides; many-sided.
   [1913 Webster]

WordNet (r) 3.0 (2006):

multilateral
    adj 1: having many parts or sides [syn: multilateral, many-
           sided] [ant: one-sided, unilateral]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "multilateral":
   bifacial, bilateral, dihedral, flanked, handed, lateral,
   many-sided, multiangular, one-sided, polygonal, polyhedral,
   prismatic, prismoid, pyramidal, pyramidic, quadrilateral, sided,
   tetrahedral, three-sided, trihedral, trilateral, triquetrous,
   two-sided, unilateral