The Collaborative International Dictionary of English v.0.48:

exogenous \ex*og"e*nous\, a.
   1. (Bot.) derived from or originating outside; pertaining to,
      or having the character of, an exogen; -- the opposite of
      endogenous.

   Syn: exogenetic.
        [1913 Webster]

   2. (Bot.) Growing by addition to the exterior; growing by
      addition of a new external layer of cells on the surface
      just beneath the bark; -- of plants.
      [1913 Webster]

   3. (Anat.) Growing from previously ossified parts; -- opposed
      to autogenous. --Owen.
      [1913 Webster]

   4. (Med.) caused by factors from outside the body, rather
      than from an abnormality of internal functions; -- of
      illness.
      [PJC]

   5. (Biol., Biochem.) not synthesized within the organism;
      absorbed or assimilated from outside the organism.
      [PJC]

   Exogenous aneurism (Med.), an aneurism which is produced by
      causes acting from without, as from injury.
      [1913 Webster]

WordNet (r) 3.0 (2006):

exogenous
    adj 1: derived or originating externally [syn: exogenous,
           exogenic] [ant: endogenic, endogenous]