nonplussed

/nษ’nหˆplสŒst/
verb
  1. 1

    To perplex or bewilder someone; to confound or flummox

adjective
  1. 1

    Bewildered; unsure how to respond or act.

  2. 2

    Unfazed, unaffected, or unimpressed.

Source: https://en.wiktionary.org/wiki/nonplus, https://en.wiktionary.org/wiki/nonplussed