Source : Webster's Revised Unabridged Dictionary (1913)

Underscore \Un`der*score"\, v. t.
   To draw a mark or line under; to underline. --J. Tucker.

Source : WordNet®

underscore
     n : a line drawn underneath (especially under written matter)
         [syn: {underline}]
     v 1: give extra weight to (a communication); "Her gesture
          emphasized her words" [syn: {underline}, {emphasize}, {emphasise}]
     2: draw a line or lines underneath to call attention to [syn: {underline}]

Source : Free On-Line Dictionary of Computing

underscore
     
         _, {ASCII} 95.
     
        Common names: {ITU-T}: underline; underscore; underbar; under.
        Rare: score; backarrow; skid; {INTERCAL}: flatworm.
     
        See also {left arrow}.
     
        (1995-03-06)