The Collaborative International Dictionary of English v.0.48:

Blacken \Black"en\, v. t. [imp. & p. p. Blackened; p. pr. &
   vb. n. Blackening.] [See Black, a., and cf. Black, v.
   t. ]
   1. To make or render black.
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            While the long funerals blacken all the way. --Pope.
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   2. To make dark; to darken; to cloud. "Blackened the whole
      heavens." --South.
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   3. To defame; to sully, as reputation; to make infamous; as,
      vice blackens the character.
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   Syn: To denigrate; defame; vilify; slander; calumniate;
        traduce; malign; asperse.
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WordNet (r) 3.0 (2006):

blackened
    adj 1: darkened by smoke; "blackened rafters"
    2: (of the face) made black especially as with suffused blood;
       "a face black with fury" [syn: black, blackened]