Gla″cial (?), a. [L. glacialis, from glacies ice: cf. F. glacial.] 1. Pertaining to ice or to its action; consisting of ice; frozen; icy; esp., pertaining to glaciers; as, glacial phenomena. Lyell.
2. (Chem.) Resembling ice; having the appearance and consistency of ice; — said of certain solid compounds; as, glacial phosphoric or acetic acids.
Glacial acid(Chem.), an acid of such strength or purity as to crystallize at an ordinary temperature, in an icelike form; as acetic or carbolic acid. — Glacial drift(Geol.), earth and rocks which have been transported by moving ice, land ice, or icebergs; bowlder drift. — Glacialepoch or period(Geol.), a period during which the climate of the modern temperate regions was polar, and ice covered large portions of the northern hemisphere to the mountain tops. — Glacialtheory or hypothesis. (Geol.) See Glacier theory, under Glacier.