1Money paid as a poll tax or capitation fee; specifically one paid by a tenant or vassal to a lord or superior. Compare "headage", head penny . Now chiefly historical.
2Money paid for each person brought, captured, killed, etc.; a financial reward offered for capturing or killing someone, a bounty; specifically money paid for each prisoner taken at sea.
Early 16th century; earliest use found in 2nd Baron Berners (c1467–1533), soldier, diplomat, and translator. From head + money.