Source : Webster's Revised Unabridged Dictionary (1913)

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.

            Whosoever committeth sin is the servant of sin.
                                                  --John viii.
                                                  34.

            Sin is the transgression of the law.  --1 John iii.
                                                  4.

            I think 't no sin. To cozen him that would unjustly
            win.                                  --Shak.

            Enthralled By sin to foul, exorbitant desires.
                                                  --Milton.

   2. An offense, in general; a violation of propriety; a
      misdemeanor; as, a sin against good manners.

            I grant that poetry's a crying sin.   --Pope.

   3. A sin offering; a sacrifice for sin.

            He hath made him to be sin for us, who knew no sin.
                                                  --2 Cor. v.
                                                  21.

   4. An embodiment of sin; a very wicked person. [R.]

            Thy ambition, Thou scarlet sin, robbed this
            bewailing land Of noble Buckingham.   --Shak.

   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.

   {Actual sin},

   {Canonical sins},

   {Original sin},

   {Venial sin}. See under {Actual}, {Canonical}, etc.

   {Deadly}, 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.

   Syn: Iniquity; wickedness; wrong. See {Crime}.

Deadly \Dead"ly\, adv.
   1. In a manner resembling, or as if produced by, death.
      ``Deadly pale.'' --Shak.

   2. In a manner to occasion death; mortally.

            The groanings of a deadly wounded man. --Ezek. xxx.
                                                  24.

   3. In an implacable manner; destructively.

   4. Extremely. [Obs.] ``Deadly weary.'' --Orrery. ``So deadly
      cunning a man.'' --Arbuthnot.

Deadly \Dead"ly\, a.
   1. Capable of causing death; mortal; fatal; destructive;
      certain or likely to cause death; as, a deadly blow or
      wound.

   2. Aiming or willing to destroy; implacable; desperately
      hostile; flagitious; as, deadly enemies.

            Thy assailant is quick, skillful, and deadly.
                                                  --Shak.

   3. Subject to death; mortal. [Obs.]

            The image of a deadly man.            --Wyclif (Rom.
                                                  i. 23).

   {Deadly nightshade} (Bot.), a poisonous plant; belladonna.
      See under {Nightshade}.

Source : WordNet®

deadly
     adv 1: as if dead [syn: {lifelessly}]
     2: as if produced by death; "deadly pale"; "a deadly paralytic
        stroke"
     3: (used as intensives) extremely; "she was madly in love";
        "deadly dull"; "deadly earnest"; "deucedly clever";
        "insanely jealous" [syn: {madly}, {insanely}, {deucedly},
        {devilishly}]
     [also: {deadliest}, {deadlier}]

deadly
     adj 1: causing or capable of causing death; "a fatal accident"; "a
            deadly enemy"; "mortal combat"; "a mortal illness"
            [syn: {deathly}, {mortal}]
     2: of an instrument of certain death; "deadly poisons"; "lethal
        weapon"; "a lethal injection" [syn: {lethal}]
     3: extremely poisonous or injurious; producing venom; "venomous
        snakes"; "a virulent insect bite" [syn: {venomous}, {virulent}]
     4: involving loss of divine grace or spiritual death; "the
        seven deadly sins" [syn: {mortal(a)}]
     5: exceedingly harmful [syn: {baneful}, {pernicious}, {pestilent}]
     6: (of a disease) having a rapid course and violent effect
     [also: {deadliest}, {deadlier}]