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