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mid-14c., "medicinal compound, antidote for poison," from Old French triacle "antidote" (c.1200), from Vulgar Latin *triacula, from Latin theriaca, from Greek theriake (antidotos) "antidote for poisonous wild animals," from fem. of theriakos "of a wild animal," from therion "wild animal," diminutive of ther (genitive theros) "wild animal," from PIE root *ghwer- "wild" (see fierce).
Sense of "molasses" is first recorded 1690s; that of "anything too sweet or sentimental" is from 1771. The connection may be from the use of molasses as a laxative, or its use to disguise the bad taste of medicine.