Source : Webster's Revised Unabridged Dictionary (1913)

Fortify \For"ti*fy\, v. t. [imp. & p. p. {Fortified}; p. pr. &
   vb. n. {Fortifying}.] [F. fortifier, L. fortificare; fortis
   strong + -ficare (in comp.) to make. See {Fort}, and {-fy}.]
   1. To add strength to; to strengthen; to confirm; to furnish
      with power to resist attack.

            Timidity was fortified by pride.      --Gibbon.

            Pride came to the aid of fancy, and both combined to
            fortify his resolution.               --Sir W.
                                                  Scott.

   2. To strengthen and secure by forts or batteries, or by
      surrounding with a wall or ditch or other military works;
      to render defensible against an attack by hostile forces.

Source : WordNet®

fortifying
     adj : invigorating physically or mentally [syn: {strengthening}]