v. To tarnish, especially someone's reputation; to debase.
the GNU version of the Collaborative International Dictionary of English
v. To smirch or soil; to discolor; to obscure. Hence: To dishonor; to sully.
The Century Dictionary and Cyclopedia
To soil; discolor, as with soot or mud; hence, to sully; obscure.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
v. smear so as to make dirty or stained
v. charge falsely or with malicious intent; attack the good name and reputation of someone
Word Usage
"GARY TUCHMAN, CNN NATIONAL CORRESPONDENT (voice-over): A warning from Michael Jackson's attorney to those who want to -- quote -- "besmirch" the king of pop's reputation."