Source : Webster's Revised Unabridged Dictionary (1913)

Throb \Throb\, v. i. [imp. & p. p. {Throbbed}; p. pr. & vb. n.
   {Throbbing}.] [OE. [thorn]robben; of uncertain origin; cf.
   Russ. trepete a trembling, and E. trepidation.]
   To beat, or pulsate, with more than usual force or rapidity;
   to beat in consequence of agitation; to palpitate; -- said of
   the heart, pulse, etc.

         My heart Throbs to know one thing.       --Shak.

         Here may his head lie on my throbbing breast. --Shak.

Source : WordNet®

throbbing
     adj : pounding or beating strongly or violently; "a throbbing
           pain"; "the throbbing engine of the boat"
     n 1: an instance of rapid strong pulsation (of the heart); "he
          felt a throbbing in his head" [syn: {throb}, {pounding}]
     2: a sound with a strong rhythmic beat; "the throbbing of the
        engines"

throb
     n 1: a deep pulsating type of pain
     2: an instance of rapid strong pulsation (of the heart); "he
        felt a throbbing in his head" [syn: {throbbing}, {pounding}]
     v 1: pulsate or pound with abnormal force; "my head is
          throbbing"; "Her heart was throbbing"
     2: expand and contract rhythmically; beat rhythmically; "The
        baby's heart was pulsating again after the surgeon
        massaged it" [syn: {pulsate}, {pulse}]
     3: tremble convulsively, as from fear or excitement [syn: {shudder},
         {shiver}, {thrill}]
     [also: {throbbing}, {throbbed}]

throbbing
     See {throb}