Old English hnecca "neck, nape, back of the neck" (a fairly rare word) from Proto-Germanic *khnekkon "the nape of the neck" (cf. Old Frisian hnekka, Middle Dutch necke, Dutch nek, Old Norse hnakkr, Old High German hnach, German Nacken "neck"), with no certain cognates outside Germanic, though Klein's sources suggest PIE *knok- "high point, ridge" (cf. Old Irish cnocc, Welsh cnwch, Old Breton cnoch "hill").
The more usual Old English words were hals (the general Germanic word, cf. Gothic, Old Norse, Danish, Swedish, Dutch, German hals), cognate with Latin collum (see collar (n.)); and swira, probably also from a PIE root meaning "column" (cf. Sanskrit svaru- "post").
Transferred senses attested from c.1400. Phrase neck of the woods (American English) is attested from 1780 in the sense of "narrow stretch of woods;" 1839 with meaning "settlement in a wooded region." To stick one's neck out "take a risk" is first recorded 1919, American English. Horses running neck and neck is attested from 1799.