"Undeniably" is a word in ENGLISH

Lat. In old Engllsh practice. Undefended; undenied by pleading. A defendant who makes no defense er plea. Blount

Not refragable; not to be gainsaid or denied; not to be refuted or overthrown; unanswerable; incontestable; undeniable; as, an irrefragable …

Those which have the value of independent words, inasmuch as the simple words are either not used at all, or …

Not deniable; incapable of denial; palpably true; indisputable; obvious; as, undeniable evidence.

Unobjectionable; unquestionably excellent; as, a person of undeniable connections.