Source : Webster's Revised Unabridged Dictionary (1913)

Shoal \Shoal\, v. t.
   To cause to become more shallow; to come to a more shallow
   part of; as, a ship shoals her water by advancing into that
   which is less deep. --Marryat.

Shoal \Shoal\, n. [AS. scolu, sceolu, a company, multitude,
   crowd, akin to OS. skola; probably originally, a division,
   and akin to Icel. skilja to part, divide. See {Skill}, and
   cf. {School}. of fishes.]
   A great multitude assembled; a crowd; a throng; -- said
   especially of fish; as, a shoal of bass. ``Great shoals of
   people.'' --Bacon.

         Beneath, a shoal of silver fishes glides. --Waller.

Shoal \Shoal\, v. i. [imp. & p. p. {Shoaled}; p. pr. & vb. n.
   {Shoaling}.]
   To assemble in a multitude; to throng; as, the fishes shoaled
   about the place. --Chapman.

Shoal \Shoal\, a. [Cf. {Shallow}; or cf. G. scholle a clod,
   glebe, OHG. scollo, scolla, prob. akin to E. shoal a
   multitude.]
   Having little depth; shallow; as, shoal water.

Shoal \Shoal\, n.
   1. A place where the water of a sea, lake, river, pond, etc.,
      is shallow; a shallow.

            The depth of your pond should be six feet; and on
            the sides some shoals for the fish to lay their
            span.                                 --Mortimer.

            Wolsey, that once trod the ways of glory, And
            sounded all the depths and shoals of honor. --Shak.

   2. A sandbank or bar which makes the water shoal.

            The god himself with ready trident stands, And opes
            the deep, and spreads the moving sands, Then heaves
            them off the shoals.                  --Dryden.

Shoal \Shoal\, v. i.
   To become shallow; as, the color of the water shows where it
   shoals.

Source : WordNet®

shoal
     n 1: a sandbank in a stretch of water that is visible at low tide
     2: a stretch of shallow water [syn: {shallow}]
     3: a large group of fish; "a school of small glittering fish
        swam by" [syn: {school}]
     v 1: make shallow; "The silt shallowed the canal" [syn: {shallow}]
     2: become shallow; "the lake shallowed over time" [syn: {shallow}]