faithlessly

comparative more faithlessly · superlative most faithlessly

1. In a faithless manner

   […]his woman, Mrs. Wargle, faithlessly consorted with Foddle, the cat's-meat man, when the steward was away, and, when he was home, cooked for him lights and liver that unquestionably were purchased from the same cat's-meat man.

   1914, Sinclair Lewis, Our Mr. Wrenn: The Romantic Adventures of a Gentle Man

   1 more example

   The concession of the King, who, be it also remembered, is a Bourbon, under such circumstances, is one of a suspicious character. Those who remember how faithlessly his father behaved in 1821, under precisely similar circumstances, to his subjects, cannot help entertaining the apprehensions that the son, like the sire, is playing fast and loose with his people, and that he will turn on them when the Austrians come to his relief.

   1848 February 12, “The Italian Question”, in The Cambridge Independent Press, Huntingdon, Bedford, & Peterborough Gazette, volume XLI, number 1,843, →OCLC, page [2], column 7