unfallible

From un- +‎ fallible.

unfallible (comparative more unfallible, superlative most unfallible)

1. Obsolete form of infallible.
   • 1591 (date written), William Shakespeare, “The First Part of Henry the Sixt”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act I, scene ii]:

     Believe my words,
     For they are certain and unfallible

• “unfallible”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.

• unfillable