Severe head pain, sharply defined, and typically described as feeling like a nail being driven into the head; usually regarded as a conversion symptom. ... Origin: L. Clavus, nail ... (05 Mar 2000) ... 
(kla´vәs his-ter´ĭ-kәs) a sharp, painful sensation as if a nail were being driven into the head, usually considered to be a conversion symptom.