[tree-k'l] properly means an antidote against the bite of wild beasts (Greek, theriaka [pharmaka], from ther a wild beast). The ancients gave the name to several sorts of anti`dotes, but ultimately it was applied chiefly to Venice treacle (thériaca androchi), a compound of some sixty-four drugs in honey.
Sir Thomas More speaks of “a most strong treacle (i.e. antidote) against these venomous heresies.” And in an old version of Jeremiah viii. 22, “balm” is translated treacle - “Is there no treacle at Gilead? Is there no phisitian there?”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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