From Middle English nape, naape, of uncertain origin. Possibly from Old French hanap, from Frankish *hnapp, from Proto-Germanic *hnappaz ( > Old English hnæpp, hnæp), as there is a hollow at the base of the skull. More at nap.
From Middle English nape, from Old French nape, nappe, from Medieval Latin nappa, napa, alteration of Latin mappa ("a cloth, napkin, towel"). More at map, apron.