An Etymological Dictionary of the German Language/Annotated/nimmer
nimmer, adverb, ‘never, never again,’ from Middle High German niemer, nimmer, nimer (from nie mêr), ‘never (of present and future actions)’; compare Modern High German nimmer in the sense of ‘no more, never again,’ for which nimmermehr is used in preference. From Middle High German niemêr, nimmêr, ‘never more.’ Both forms are derivatives of Old High German nio and mêr (like Anglo-Saxon nœ̂fre, English never, from *nâmire); nimmermehr contains the second component twice. See nicht and nie.