The Collaborative International Dictionary of English v.0.48:

Hot-head \Hot"-head`\, n.
   A violent, passionate person; a hasty or impetuous person;
   as, the rant of a hot-head.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hothead
    n 1: a belligerent grouch [syn: fire-eater, hothead]
    2: a reckless impetuous irresponsible person [syn: daredevil,
       madcap, hothead, swashbuckler, lunatic, harum-
       scarum]