undoubtably

From Middle English undoutably, equivalent to undoubtable +‎ -ly.

undoubtably (not comparable)

1. (sometimes considered nonstandard) Without doubt; indubitably, undoubtedly.
   • 1679, Edmund Everard, Discourses on the present state of the Protestant princes of Europe, London: Dorman Newman, page 20:

     I leave it to all the Protestant Princes of Europe to judge if their safety can be solidly established in their Leagues and Confederations with the Princes of the Roman Communion, as it may be undoubtably effected by their Leagues and Confederations amongst themselves.

   • 1887, Albert Parsons, Autobiography:

     This method would undoubtably strike a wholesome terror into the hearts of the working classes.

   • 1963 October 5, Charles Poore, “Books of The Times: The Curtain Speeches of Somerset Maugham”, in New York Times, page 18:

     Maugham suggests that storytelling began when primeval hunters told tales around their fires and turbaned raconteurs held forth in what Sinclair Lewis called the clattering bright bazaars. He's undoubtably right.

   • 2003, M. Van Atten, J. Kennedy, “On the Philosophical Development of Kurt Gödel”, in The Bulletin of Symbolic Logic, volume 9, number 4, page 431:

     Thus, by analogy, philosophical propositions will involve primitive terms, to be arrived at, undoubtably, by a kind of conceptual analysis.

• "Undoubtably" is considered to be nonstandard English by some authorities (for example, Garner's Modern American Usage (2009)), and the term is seldom found in modern literary writing.[1] The Oxford English Dictionary provides no examples of usage after 1513 and characterizes "undoubtably" as "? Obs.," wondering whether the term is obsolete.[2] Nevertheless, many examples of its usage can be found in 20th- and 21st-century popular English and in contemporary academic journals. Its persistence in use may reflect that some writers wish to draw an epistemic differentiability between the idea of "I don't doubt X" or "hardly anyone doubts X" (undoubtedly) versus "it is impossible or nonsensical to doubt X" (undoubtably), where the latter is a stronger category of dubiousness (this differentiation is analogous to that between, for example, undetected and undetectable). But the desired differentiation is not well established or standard.

• indubitably, undoubtedly, doubtlessly, unquestionably