The Collaborative International Dictionary of English v.0.48:

Blemish \Blem"ish\, v. t. [imp. & p. p. Blemished; p. pr. &
   vb. n. Blemishing.] [OE. blemissen, blemishen, OF. blemir,
   blesmir, to strike, injure, soil, F. bl[^e]mir to grow pale,
   fr. OF. bleme, blesme, pale, wan, F. bl[^e]me, prob. fr. Icel
   bl[=a]man the livid color of a wound, fr. bl[=a]r blue; akin
   to E. blue. OF. blemir properly signifies to beat one (black
   and) blue, and to render blue or dirty. See Blue.]
   1. To mark with deformity; to injure or impair, as anything
      which is well formed, or excellent; to mar, or make
      defective, either the body or mind.
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            Sin is a soil which blemisheth the beauty of thy
            soul.                                 --Brathwait.
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   2. To tarnish, as reputation or character; to defame.
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            There had nothing passed between us that might
            blemish reputation.                   --Oldys.
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