The Collaborative International Dictionary of English v.0.48:

Adrenaline \Ad*re"nal*ine\, n. Also Adrenalin \Ad*re"nal*in\
   (Physiol. Chem.)
   a hormone secreted by the adrenal medulla that acts as a
   powerful stimulant in reponse to fear or stress; it
   stimulates autonomic nerve action. It can be obtained as a
   crystalline substance, C9H13NO3. It is used in medicine as
   a vasoconstrictor (hemostatic) and cardiac stimulant, also to
   reduce allergic reactions and to stimulate the heart in cases
   of cardiac arrest. --MI11

   Syn: epinephrine;
        3,4-dihydroxy-1-[1-hydroxy-2-(methylamino)-ethyl]benzene.
        [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

Adrenalin
    n 1: a catecholamine secreted by the adrenal medulla in response
         to stress (trade name Adrenalin); stimulates autonomic
         nerve action [syn: epinephrine, epinephrin,
         adrenaline, Adrenalin]