"B" Is For ...

Besmirch. verb. trans.

From the Shorter Oxford English Dictionary (my latest acquisition): Dull or discolor, as with smoke or mud; dim the brightness of; and fig. sully (as in a reputation); besmutch.

From Wikitionary: additionally, to tarnish

and Wiki breaks it down further into the various verb usages - third person singular simple present" besmirches; present participle: besmirching; and simple past and past participle: besmirched.

similarly from the OED:

Besmear. verb. trans. (smear over, cover or soil with a greasy or stick substance; sully or defame.

Beslubber (verb trans.) smear or daub over with liquid or sticky matter.

and, my favorite:

Besmut (verb. trans) - blacken as with soot; defame.

And from MSN Encarta: Synonyms - sully, defame, tarnish, damage, slander, and drag through the mud. Antonym - praise