posthorn

/P OW1 S T ER0 N/
noun
  1. 1

    A type of brass horn used to signal the arrival or departure of a postrider or mailcoach.

  2. 2

    A valveless musical instrument based on such a horn, used in orchestral music.

Source: https://en.wiktionary.org/wiki/post%20horn, https://en.wiktionary.org/wiki/posthorn