English: from the Middle English (Old French) personal name Denis(e), Dinis(e), vernacular forms of Latin Dionysius, Greek Dionysios ‘(follower) of Dionysos’, an eastern god introduced to the classical pantheon at a relatively late date and bearing a name of probably Semitic origin. The name was borne by various early Christian saints, including Saint Denis, the martyred 3rd-century bishop of Paris who became the patron saint of France. From the 12th century onward, the popularity of the name in England (and of its cognates, mainly Denis , in the continental Europe) seems to have been largely due to French influence. The feminine form Dionysia (in vernacular English likewise Den(n)is) is also found, and some examples of the surname may originate from it.

English: from Middle English deneis, a variant of danais ‘Danish’, with the vowel influenced by Middle English denshe (Old English denisc). Compare Dence .

Irish (mainly Dublin and Cork): of the same origin as 1 and 2 above, sometimes an alternative form to Donohue but more often to McDonough , since the personal name Donnchadh was Anglicized as Donough or Denis.