"chalky mineral used in making mortar," from Old English lim "sticky substance, birdlime, mortar, cement, gluten," from Proto-Germanic *leimaz (cf. Old Saxon, Old Norse, Danish lim, Dutch lijm, German Leim "birdlime"), from PIE root *(s)lei- "slime, slimy, sticky" (cf. Latin limus "slime, mud, mire," linere "to smear;" see slime (n.)). Lime is made by putting limestone or shells in a red heat, which burns off the carbonic acid and leaves a brittle white solid which dissolves easily in water. Hence lime-kiln (late 13c.), lime-burner (early 14c.). As a verb, c.1200, from the noun.