noun
Refers to the back of the neck, especially when grabbed or held. Often used in the phrase 首根っこ (くびねっこ).
猫の首根をつかんで持ち上げた。
I grabbed the cat by the scruff of its neck and lifted it up.
彼は弟の首根っこを押さえて動かした。
He grabbed his younger brother by the scruff of the neck and moved him.
Colloquial form with the same meaning, often used in casual speech.
Compound of 首 (くび, 'neck') and 根 (ね, 'root, base'). The exact historical derivation is uncertain, but the combination naturally refers to the base of the neck.