Theodore Clarke Smith, when comparing the Book of Mormon and the Spalding Manuscript, argues that the use of "adieu" in both volumes are anachronistic.
Theodore Clarke Smith, The External Evidences of the Book of Mormon (N.P.: Theodore Clarke Smith, 1912), 94
(4 ) In both books the word "adieu,' is used. Twice in the Ms. and in the B. M. Jacob ends his book with, "Brethren, adieu ." A French word appearing many hundreds of years before the French language was spoken.