freshly severed head
Refers specifically to a head that has just been cut off, often in historical or violent contexts. Not used for a living head or a skull.
Paintings from the Warring States period sometimes depict freshly severed heads.
Compound of 生 (なま, 'raw, fresh') and 首 (くび, 'head, neck'). The exact historical derivation is uncertain, but the meaning is transparent from its components.