Source : Webster's Revised Unabridged Dictionary (1913)

Foe \Foe\ (f[=o]), n. [OE. fo, fa, AS. f[=a]h hostile; prob.
   akin to E. fiend. [root]81. See {Fiend}, and cf. {Feud} a
   quarrel.]
   1. One who entertains personal enmity, hatred, grudge, or
      malice, against another; an enemy.

            A man's foes shall be they of his own household.
                                                  --Matt. x. 36

   2. An enemy in war; a hostile army.

   3. One who opposes on principle; an opponent; an adversary;
      an ill-wisher; as, a foe to religion.

            A foe to received doctrines.          --I. Watts

Foe \Foe\, v. t.
   To treat as an enemy. [Obs.] --Spenser.

Source : WordNet®

foe
     n 1: an armed adversary (especially a member of an opposing
          military force); "a soldier must be prepared to kill his
          enemies" [syn: {enemy}, {foeman}, {opposition}]
     2: a personal enemy; "they had been political foes for years"
        [syn: {enemy}] [ant: {ally}]