The Collaborative International Dictionary of English v.0.48:

Groan \Groan\, v. t.
   To affect by groans.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Such groans of roaring wind and rain.    --Shak.
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         The wretched animal heaved forth such groans. --Shak.
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The Collaborative International Dictionary of English v.0.48:

groan \groan\ (gr[=o]n), v. i. [imp. & p. p. Groaned
   (gr[=o]nd); p. pr. & vb. n. Groaning.] [OE. gronen, granen,
   granien, AS. gr[=a]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.
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            For we . . . do groan, being burdened. --2 Cor. v.
                                                  4.
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            He heard the groaning of the oak.     --Sir W.
                                                  Scott.
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   2. To strive after earnestly, as with groans.
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            Nothing but holy, pure, and clear,
            Or that which groaneth to be so.      --Herbert.
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WordNet (r) 3.0 (2006):

groan
    n 1: an utterance expressing pain or disapproval [syn: groan,
         moan]
    v 1: indicate pain, discomfort, or displeasure; "The students
         groaned when the professor got out the exam booklets"; "The
         ancient door soughed when opened" [syn: groan, moan]