Source : Webster's Revised Unabridged Dictionary (1913)

Outmost \Out"most`\, a. [OE. outemest, utmest, AS. ?temest, a
   superl. fr. ?te out. See {Out}, {Utmost}, and cf.
   {Outermost}.]
   Farthest from the middle or interior; farthest outward;
   outermost.

Source : WordNet®

outmost
     adj : situated at the farthest possible point from a center [syn:
           {outermost}]