impugn vs slur

impugn

verb
  • To verbally assault, especially to argue against an opinion, motive, or action; to question the truth or validity of. 

slur

verb
  • To insult or slight. 

  • To run together; to articulate poorly. 

  • To play legato or without separate articulation; to connect (notes) smoothly. 

  • To soil; to sully; to contaminate; to disgrace. 

  • To cover over; to disguise; to conceal; to pass over lightly or with little notice. 

  • To cheat, as by sliding a die; to trick. 

noun
  • In knitting machines, a device for depressing the sinkers successively by passing over them. 

  • An insinuation or innuendo. 

  • An act of running one's words together; poor verbal articulation. 

  • A mark, stain, or smear; (by extension) a slight occasion of reproach. 

  • A disparaging insult or slight, particularly one used to denigrate a specific group. 

  • A set of notes that are played legato, without separate articulation. 

  • The symbol indicating a legato passage, written as an arc over the slurred notes (not to be confused with a tie). 

How often have the words impugn and slur occurred in a corpus of books? (source: Google Ngram Viewer )