treacle n.

mid-14c., "medicinal compound, antidote for poison," from Old French triacle "antidote, cure for snake-bite" (c. 1200), from Vulgar Latin *triacula, from Latin theriaca, from Greek thēriakē (antidotos) "antidote for poisonous wild animals," from fem. of thēriakos "of a wild animal," from thērion "wild animal," diminutive of thēr (genitive thēros) "wild animal," from PIE root *ghwer- "wild beast."

The sense of "molasses" is recorded from 1690s (the connection may be from the use of molasses as a laxative, or its use to disguise the bad taste of medicine); that of "anything too sweet or sentimental" is from 1771. Related: Treacly.