Use the adjective treacly to describe something that has a sticky, sweet flavor. Your dad's chocolate pecan pie might be a little too treacly for your taste.
Something that's way too sugary is treacly. Your little brother might love treats like fudge and caramels and syrupy soft drinks that just taste treacly to you. You can also use the word in a more figurative way, to talk about overly sweet talk or behavior, like the treacly language on a sentimental greeting card. Treacly comes from treacle — a British term for molasses — originally "an antidote to poison," from the Greek root theriake, "antidote for poisonous wild animals."