False Note Meaning

(idiomatic, by extension) In a non-verbal display or presentation, an indication of incongruity or inappropriateness.

Example: 1819, Washington Irving, "The Lovers" in Bracebridge Hall:
  Sometimes he even thrums a little on the piano, and takes a part in a trio, in which his voice can generally be distinguished by a certain quavering tone, and an occasional false note.
1860, Wilkie Collins, The Woman in White, ch. 15:
  Her fingers wavered on the piano—she struck a false note, confused herself in trying to set it right, and dropped her hands angrily on her lap.
1900, Fergus Hume, The Bishop's Secret, ch. 25:
  [H]is words were grave, his manner was earnest, and his speech came from the fulness of his heart. If there had been a false note, a false look, Harry would have detected both.
1990 Sep. 14, Janet Maslin, "Movie Review: White Hunter Black Heart (1990)," New York Times (retrieved 16 April 2015):
  The screenplay . . . even suggests that this contributed to the false note on which The African Queen actually ends.
2010 Dec. 10, Brigitte Weeks, "Book World: From its opening car crash, Anita Shreve's character-driven Rescue is worth the ride," Washington Post (retrieved 16 April 2015):
  Shreve creates a little world, peoples it with believable characters, and puts them through agonizing and joyful moments without a false note or a dissonant figure of speech.
2009 Feb. 20, Hilary Alexander, "London Fashion Week: Caroline Charles," Telegraph (UK) (retrieved 16 April 2015):
  The only false note in an otherwise classic and elegant collection was the gratuitous flash of black fishnet stockings and suspenders under otherwise unremarkable paisley and floral shirts.