We don't have synonyms for copal yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are coal, coral and comal.
(n) :
a resinous exudation from various tropical trees that is collected from living trees or dug from the ground as a fossil, that when hard must be rendered soluble in alcohol and other organic solvents by heating, and that is used chiefly in making varnishes and printing ink
(n) :
a resinous exudation from various tropical trees that is collected from living trees or dug from the ground as a fossil, that when hard must be rendered soluble in alcohol and other organic solvents by heating, and that is used chiefly in making varnishes and printing ink