The Collaborative International Dictionary of English v.0.48:

Sin \Sin\, n. [OE. sinne, AS. synn, syn; akin to D. zonde, OS.
   sundia, OHG. sunta, G. s["u]nde, Icel., Dan. & Sw. synd, L.
   sons, sontis, guilty, perhaps originally from the p. pr. of
   the verb signifying, to be, and meaning, the one who it is.
   Cf. Authentic, Sooth.]
   1. Transgression of the law of God; disobedience of the
      divine command; any violation of God's will, either in
      purpose or conduct; moral deficiency in the character;
      iniquity; as, sins of omission and sins of commission.
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            Whosoever committeth sin is the servant of sin.
                                                  --John viii.
                                                  34.
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            Sin is the transgression of the law.  --1 John iii.
                                                  4.
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            I think 't no sin.
            To cozen him that would unjustly win. --Shak.
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            Enthralled
            By sin to foul, exorbitant desires.   --Milton.
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   2. An offense, in general; a violation of propriety; a
      misdemeanor; as, a sin against good manners.
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            I grant that poetry's a crying sin.   --Pope.
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   3. A sin offering; a sacrifice for sin.
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            He hath made him to be sin for us, who knew no sin.
                                                  --2 Cor. v.
                                                  21.
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   4. An embodiment of sin; a very wicked person. [R.]
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            Thy ambition,
            Thou scarlet sin, robbed this bewailing land
            Of noble Buckingham.                  --Shak.
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   Note: Sin is used in the formation of some compound words of
         obvious signification; as, sin-born; sin-bred,
         sin-oppressed, sin-polluted, and the like.
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   Actual sin, Canonical sins, Original sin, Venial sin.
      See under Actual, Canonical, etc.

   Deadly sins, or Mortal sins (R. C. Ch.), willful and
      deliberate transgressions, which take away divine grace;
      -- in distinction from vental sins. The seven deadly sins
      are pride, covetousness, lust, wrath, gluttony, envy, and
      sloth.

   Sin eater, a man who (according to a former practice in
      England) for a small gratuity ate a piece of bread laid on
      the chest of a dead person, whereby he was supposed to
      have taken the sins of the dead person upon himself.

   Sin offering, a sacrifice for sin; something offered as an
      expiation for sin.
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   Syn: Iniquity; wickedness; wrong. See Crime.
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The Collaborative International Dictionary of English v.0.48:

Sin \Sin\, adv., prep., & conj.
   Old form of Since. [Obs. or Prov. Eng. & Scot.]
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         Sin that his lord was twenty year of age. --Chaucer.
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The Collaborative International Dictionary of English v.0.48:

Sin \Sin\, v. i. [imp. & p. p. Sinned; p. pr. & vb. n.
   Sinning.] [OE. sinnen, singen, sinegen, AS. syngian. See
   Sin, n.]
   1. To depart voluntarily from the path of duty prescribed by
      God to man; to violate the divine law in any particular,
      by actual transgression or by the neglect or nonobservance
      of its injunctions; to violate any known rule of duty; --
      often followed by against.
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            Against thee, thee only, have I sinned. --Ps. li. 4.
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            All have sinned, and come short of the glory of God.
                                                  --Rom. iii.
                                                  23.
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   2. To violate human rights, law, or propriety; to commit an
      offense; to trespass; to transgress.
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            I am a man
            More sinned against than sinning.     --Shak.
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            Who but wishes to invert the laws
            Of order, sins against the eternal cause. --Pope.
      [1913 Webster] Sinaic

WordNet (r) 3.0 (2006):

sin
    n 1: estrangement from god [syn: sin, sinfulness,
         wickedness]
    2: an act that is regarded by theologians as a transgression of
       God's will [syn: sin, sinning]
    3: ratio of the length of the side opposite the given angle to
       the length of the hypotenuse of a right-angled triangle [syn:
       sine, sin]
    4: (Akkadian) god of the Moon; counterpart of Sumerian Nanna
    5: the 21st letter of the Hebrew alphabet
    6: violent and excited activity; "they began to fight like sin"
       [syn: sin, hell]
    v 1: commit a sin; violate a law of God or a moral law [syn:
         sin, transgress, trespass]
    2: commit a faux pas or a fault or make a serious mistake; "I
       blundered during the job interview" [syn: drop the ball,
       sin, blunder, boob, goof]