noun
hair at the nape of the neck; scruff of the neck
Refers to the hair growing at the back of the neck, often mentioned in contexts of grabbing or cutting.
彼は襟髪を掴まれて引きずられた。
He was dragged by the scruff of his neck.
襟髪が伸びてきたので、散髪に行く。
The hair on my nape has grown long, so I'm going to get a haircut.
襟足 refers to the hairline or the lower part of the back of the head, often used in hairdressing contexts, while 襟髪 specifically emphasizes the hair itself at the nape.
Compound of 襟 (eri, 'collar, neck') and 髪 (kami, 'hair'), with rendaku voicing of 髪 to がみ. The exact historical derivation is uncertain, but the word straightforwardly describes the hair at the nape.