Source : Webster's Revised Unabridged Dictionary (1913)

Deep \Deep\ (d[=e]p), a. [Compar. {Deeper}; superl. {Deepest}.]
   [OE. dep, deop, AS. de['o]p; akin to D. diep, G. tief, Icel.
   dj[=u]pr, Sw. diup, Dan. dyb, Goth. diups; fr. the root of E.
   dip, dive. See {Dip}, {Dive}.]
   1. 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.

            The water where the brook is deep.    --Shak.

   2. 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.

            Shadowing squadrons deep.             --Milton.

            Safely in harbor Is the king's ship in the deep
            nook.                                 --Shak.

   3. Low in situation; lying far below the general surface; as,
      a deep valley.

   4. Hard to penetrate or comprehend; profound; -- opposed to
      shallow or superficial; intricate; mysterious; not
      obvious; obscure; as, a deep subject or plot.

            Speculations high or deep.            --Milton.

            A question deep almost as the mystery of life. --De
                                                  Quincey.

            O Lord, . . . thy thoughts are very deep. --Ps.
                                                  xcii. 5.

   5. Of penetrating or far-reaching intellect; not superficial;
      thoroughly skilled; sagacious; cunning.

            Deep clerks she dumbs.                --Shak.

   6. Profound; thorough; complete; unmixed; intense; heavy;
      heartfelt; as, deep distress; deep melancholy; deep
      horror. ``Deep despair.'' --Milton. ``Deep silence.''
      --Milton. ``Deep sleep.'' --Gen. ii. 21. ``Deeper
      darkness.'' -->Hoole. ``Their deep poverty.'' --2 Cor.
      viii. 2.

            An attitude of deep respect.          --Motley.

   7. Strongly colored; dark; intense; not light or thin; as,
      deep blue or crimson.

   8. Of low tone; full-toned; not high or sharp; grave; heavy.
      ``The deep thunder.'' --Byron.

            The bass of heaven's deep organ.      --Milton.

   9. Muddy; boggy; sandy; -- said of roads. --Chaucer.

            The ways in that vale were very deep. --Clarendon.

   {A deep line of operations} (Military), a long line.

   {Deep mourning} (Costume), mourning complete and strongly
      marked, the garments being not only all black, but also
      composed of lusterless materials and of such fashion as is
      identified with mourning garments.