Source : Webster's Revised Unabridged Dictionary (1913)

-gen \-gen\ [(1) From Gr. -gen-, from the same root as ge`nos
   race, stock (see {Genus}). (2) From Gr. suffix -genh`s born.
   Cf. F. -g[`e]ne.]
   1. A suffix used in scientific words in the sense of
      producing, generating: as, amphigen, amidogen, halogen.

   2. A suffix meaning produced, generated; as, exogen.