gla·cial / ˈglāshəl/ • adj. 1. relating to, resulting from, or denoting the presence or agency of ice, esp. in the form of glaciers: thick glacial deposits a glacial lake.2. of ice; icy: the glacial mountains of New Zealand | fig. glacial blue eyes. ∎  extremely cold: glacial temperatures. ∎  Chem. denoting pure organic acids (esp. acetic acid) that form icelike crystals on freezing. ∎  extremely slow (like the movement of a glacier): an official described progress in the talks as glacial.• n. Geol. a glacial period.DERIVATIVES: gla·cial·ly adv.

glacial XVII. — F. glacial or L. glaciālis icy, f. glaciēs ice; see -AL1.