Artificial intelligent assistant

infailable

inˈfailable, a. Obs.
  Also 7 infaillible.
  [in-3. Partly, at least, a. F. infaillible (15th c.).]
  Not liable to fail; unfailing; reliable; infallible.

1561 Eden Arte of Nauig. Pref. {fatpara}{fatpara} ij, Certain infaileable sygnes and tokens of the same. Ibid. A ij b, Infaylable principles. 1631 Denison Heav. Banq. 47 Liuely and infaillible signes of the presence of Christ. Ibid. 106 A few..infaillible markes, wherby we may know whether wee haue receiued Christ.

Oxford English Dictionary

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