Source : Webster's Revised Unabridged Dictionary (1913)

Agonize \Ag"o*nize\, v. i. [imp. & p. p. {Agonized}; p. pr. &
   vb. n. {Agonizing}.] [F. agoniser, LL. agonizare, fr. Gr. ?.
   See {Agony}.]
   1. To writhe with agony; to suffer violent anguish.

            To smart and agonize at every pore.   --Pope.

   2. To struggle; to wrestle; to strive desperately.

Source : WordNet®

agonizing
     adj : extremely painful [syn: {agonising}, {excruciating}, {harrowing},
            {torturing}, {torturous}, {torturesome}]