Source : Webster's Revised Unabridged Dictionary (1913)

Generalissimo \Gen`er*al*is"si*mo\, n. [It., superl. of generale
   general. See {General}, a.]
   The chief commander of an army; especially, the commander in
   chief of an army consisting of two or more grand divisions
   under separate commanders; -- a title used in most foreign
   countries.

Source : WordNet®

generalissimo
     n : the officer who holds the supreme command; "in the U.S. the
         president is the commander in chief" [syn: {commander in
         chief}]