The Collaborative International Dictionary of English v.0.48:

Apothegm \Ap"o*thegm\, Apophthegm \Ap"oph*thegm\, n. [Gr.
   'apo`fqegma thing uttered, apothegm, from 'apofqe`ggesqai to
   speak out; 'apo` from + fqe`ggesqai to speak.]
   A short, pithy, and instructive saying; a terse remark,
   conveying some important truth; a sententious precept or
   maxim.

   Note: [Apothegm is now the prevalent spelling in the United
         States.]
         [1913 Webster] Apothegmatic

The Collaborative International Dictionary of English v.0.48:

Apophthegm \Ap`oph*thegm\, n.
   See Apothegm.
   [1913 Webster] Apophthegmatic

WordNet (r) 3.0 (2006):

apophthegm
    n 1: a short pithy instructive saying [syn: aphorism,
         apothegm, apophthegm]