From 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]From WordNet (r) 3.0 (2006) :
copal n 1: a brittle aromatic resin used in varnishes