(transitive) to defame; slander (esp in the phrase blacken someone's name)
Word Origin and History for blacken
v.
c.1200, "become black or dark;" early 14c., "make black, darken, dye (hair);" see black + -en (1). Figurative sense of "to besmirch" (with dishonor, etc.) is from early 15c. Related: Blackened; blackening.