Source : Webster's Revised Unabridged Dictionary (1913)

Dig \Dig\, v. i.
   1. To work hard or drudge; specif. (U. S.): To study
      ploddingly and laboriously. [Colloq.]

            Peter dug at his books all the harder. --Paul L.
                                                  Ford.

   2. (Mach.) Of a tool: To cut deeply into the work because ill
      set, held at a wrong angle, or the like, as when a lathe
      tool is set too low and so sprung into the work.

   {To dig out}, to depart; to leave, esp. hastily; decamp.
      [Slang, U. S.]