The Collaborative International Dictionary of English v.0.48:

Copal \Co"pal\ (k[=o]"pal; 277), [Sp., fr. Mexican copalli, a
   generic name of resins. --Clavigero.]
   A resinous substance flowing spontaneously from trees of
   Zanzibar, Madagascar, and South America (Trachylobium
   Hornemannianum, Trachylobium verrucosum, and Hymen[ae]a
   Courbaril), and dug from earth where forests have stood in
   Africa; -- used chiefly in making varnishes. --Ure.
   [1913 Webster]

WordNet (r) 3.0 (2006):

copal
    n 1: a brittle aromatic resin used in varnishes