Source : Webster's Revised Unabridged Dictionary (1913)

Groan \Groan\, v. t.
   To affect by groans.

Groan \Groan\, n.
   A low, moaning sound; usually, a deep, mournful sound uttered
   in pain or great distress; sometimes, an expression of strong
   disapprobation; as, the remark was received with groans.

         Such groans of roaring wind and rain.    --Shak.

         The wretched animal heaved forth such groans. --Shak.

Groan \Groan\, v. i. [imp. & p. p. {Groaned}; p. pr. & vb. n.
   {Groaning}.] [OE. gronen, granen, granien, AS. gr?nian, fr.
   the root of grennian to grin. [root]35. See {2d Grin}, and
   cf. {Grunt}.]
   1. To give forth a low, moaning sound in breathing; to utter
      a groan, as in pain, in sorrow, or in derision; to moan.

            For we . . . do groan, being burdened. --2 Cor. v.
                                                  4.

            He heard the groaning of the oak.     --Sir W.
                                                  Scott.

   2. To strive after earnestly, as with groans.

            Nothing but holy, pure, and clear, Or that which
            groaneth to be so.                    --Herbert.

Source : WordNet®

groan
     n : an utterance expressing pain or disapproval [syn: {moan}]
     v : indicate pain, discomfort, or displeasure; "The students
         groaned when the professor got out the exam booklets";
         "The ancient door soughed when opened" [syn: {moan}, {sough}]