before vowels, gluc-, word-forming element used since c. 1880s, a later form of glyco-, from Greek glykys "sweet," figuratively "delightful; dear; simple, silly," from *glku-, a dissimilation in Greek from PIE root *dlk-u- "sweet" (source also of Latin dulcis). De Vaan writes that "It is likely that we are dealing with a common borrowing from an unknown source." Now usually with reference to glucose.
Entries linking to gluco-
glyco-
before vowels glyc-, word-forming element meaning "sweet," from Latinized combining form of Greek glykys, glykeros "sweet" (see gluco-). Used in reference to sugars generally. OED says a regular formation would be glycy-.
dulcet adj.
"sweet to the senses," especially of taste, also "melodious, harmonious," late 14c., doucet, from Old French doucet, diminutive of doux "sweet," earlier dulz, from Latin dulcis, from Proto-Italic *dulkwi-, from PIE *dlk-wi-, suffixed form of root *dlk-u- "sweet," which probably is also the source of Greek glykys "sweet" (compare gluco-).