The Collaborative International Dictionary of English v.0.48:

Organon \Or"ga*non\, Organum \Or"ga*num\, n. [NL. organon, L.
   organum. See Organ.]
   An organ or instrument; hence, a method by which
   philosophical or scientific investigation may be conducted;
   -- a term adopted from the Aristotelian writers by Lord
   Bacon, as the title ("Novum Organon") of part of his treatise
   on philosophical method. --Sir. W. Hamilton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

organon
    n 1: a system of principles for philosophic or scientific
         investigations; an instrument for acquiring knowledge