The Collaborative International Dictionary of English v.0.48:

Moan \Moan\, v. t.
   1. To bewail audibly; to lament.
      [1913 Webster]

            Ye floods, ye woods, ye echoes, moan
            My dear Columbo, dead and gone.       --Prior.
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   2. To afflict; to distress. [Obs.]
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            Which infinitely moans me.            --Beau. & Fl.
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The Collaborative International Dictionary of English v.0.48:

Moan \Moan\ (m[=o]n), v. i. [imp. & p. p. Moaned (m[=o]nd); p.
   pr. & vb. n. Moaning.] [AS. m[=ae]nan to moan, also, to
   mean; but in the latter sense perh. a different word. Cf.
   Mean to intend.]
   1. To make a low prolonged sound of grief or pain, whether
      articulate or not; to groan softly and continuously.
      [1913 Webster]

            Unpitied and unheard, where misery moans. --Thomson.
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            Let there bechance him pitiful mischances,
            To make him moan.                     --Shak.
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   2. To emit a sound like moan; -- said of things inanimate;
      as, the wind moans.
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The Collaborative International Dictionary of English v.0.48:

Moan \Moan\, n. [OE. mone. See Moan, v. i.]
   1. A low prolonged sound, articulate or not, indicative of
      pain or of grief; a low groan.
      [1913 Webster]

            Sullen moans, hollow groans.          --Pope.
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   2. A low mournful or murmuring sound; -- of things.
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            Rippling waters made a pleasant moan. --Byron.
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WordNet (r) 3.0 (2006):

moan
    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]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "moan":
   bawl, beef, bemoan, bewail, bitch, complain, complaint, cry,
   cry out, deplore, dirge, dolorous tirade, elegize,
   give sorrow words, grievance, grieve, gripe, groan, grouse, growl,
   grumble, howl, jeremiad, keen, knell, lament, lamentation,
   make an outcry, mewl, moaning, mourn, murmur, mutter, outcry, pipe,
   plaint, planctus, pule, repine, roar, scream, screech, shriek,
   sigh, sing, sing the blues, snarl, snivel, sob, sorrow, sough,
   squall, tirade, ululate, ululation, wail, wail of woe, weep,
   weep over, whimper, whine, whisper, whistle, yawl, yawp, yell,
   yowl