"viscous adhesive substance," early 13c., from Old French glu "glue, birdlime" (12c.), from Vulgar Latin *glutis or Late Latin glutem (nominative glus) "glue," from Latin gluten "glue, beeswax," from PIE *gleit- "to glue, paste" (source also of Lithuanian glitus "sticky," glitas "mucus;" Old English cliða "plaster"), from root *glei- "clay," also forming words with a sense of "to stick together" (see clay).

Gluten, Latin word for glue, is a protein found in all forms of wheat (durum, semolina, spelt, kamut, einkorn, and faro) and other grains including rye, barley, and triticale. Ideal for baked goods, gluten makes the dough spongy and elastic, giving it the strength and consistency needed to retain its shape and fluffiness.

1580s, "unite or cause to adhere," from Latin agglutinatus, past participle of agglutinare "fasten with glue," from ad "to" (see ad-) + glutinare "to glue," from gluten "glue" (from PIE *glei-; see glue (n.)).