Treacle is particularly British; similar substances may have different names in other forms of English. In the UK, treacle scones are a popular treat.
Pro Tip 2/3
Syrup Density
Treacle is denser than water so it pours slowly, often used as a metaphor for sluggishness. Time moved like treacle as he awaited her reply.
Pro Tip 3/3
Not Always Sweet
While treacle is sweet, in context it can refer to something overly or sickeningly sweet. Her treacle-like words couldn't mask the bitterness of her actions.