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.
      [1913 Webster]

            Against thee, thee only, have I sinned. --Ps. li. 4.
      [1913 Webster]

            All have sinned, and come short of the glory of God.
                                                  --Rom. iii.
                                                  23.
      [1913 Webster]

   2. To violate human rights, law, or propriety; to commit an
      offense; to trespass; to transgress.
      [1913 Webster]

            I am a man
            More sinned against than sinning.     --Shak.
      [1913 Webster]

            Who but wishes to invert the laws
            Of order, sins against the eternal cause. --Pope.
      [1913 Webster] Sinaic

WordNet (r) 3.0 (2006):

sinning
    adj 1: transgressing a moral or divine law; "if it be a sin to
           covet honor, I am the most sinning soul alive"-
           Shakespeare
    n 1: an act that is regarded by theologians as a transgression
         of God's will [syn: sin, sinning]