Douglas Harper's Etymology Dictionary
glyco-
word-forming element meaning "sweet," from Latinized comb. form of Greek glykys "sweet" (see glucose). Used in reference to sugars generally. OED says a regular formation would be glycy-.
Wiktionary
glyco-
pre. 1 (non-gloss definition: Forms terms relating to sugars.) 2 (non-gloss definition: Forms terms relating to glycogen.)