The Collaborative International Dictionary of English v.0.48:

Mar \Mar\, v. t. [imp. & p. p. Marred (m[aum]rd); p. pr. & vb.
   n. Marring.] [OE. marren, merren, AS. merran, myrran (in
   comp.), to obstruct, impede, dissipate; akin to OS. merrian,
   OHG. marrjan, merran; cf. D. marren, meeren, to moor a ship,
   Icel. merja to bruise, crush, and Goth. marzjan to offend.
   Cf. Moor, v.]
   1. To make defective; to do injury to, esp. by cutting off or
      defacing a part; to impair; to disfigure; to deface.
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            I pray you mar no more trees with wiring love songs
            in their barks.                       --Shak.
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            But mirth is marred, and the good cheer is lost.
                                                  --Dryden.
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            Ire, envy, and despair
            Which marred all his borrowed visage. --Milton.
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   2. To spoil; to ruin. "It makes us, or it mars us." "Striving
      to mend, to mar the subject." --Shak.
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