extending far below the surface; of great perpendicular dimension (measured from the surface downward, and distinguished from high, which is measured upward); far to the bottom; having a certain depth; as, a deep sea.-extending far back from the front or outer part; of great horizontal dimension (measured backward from the front or nearer part, mouth, etc.); as, a deep cave or recess or wound; a gallery ten seats deep; a company of soldiers six files deep.-low in situation; lying far below the general surface; as, a deep valley.-hard to penetrate or comprehend; profound; -- opposed to shallow or superficial; intricate; mysterious; not obvious; obscure; as, a deep subject or plot.-of penetrating or far-reaching intellect; not superficial; thoroughly skilled; sagacious; cunning.-profound; thorough; complete; unmixed; intense; heavy; heartfelt; as, deep distress; deep melancholy; deep horror.-strongly colored; dark; intense; not light or thin; as, deep blue or crimson.-of low tone; full-toned; not high or sharp; grave; heavy.-muddy; boggy; sandy; -- said of roads.-to a great depth; with depth; far down; profoundly; deeply.-that which is deep, especially deep water, as the sea or ocean; an abyss; a great depth.-that which is profound, not easily fathomed, or incomprehensible; a moral or spiritual depth or abyss.