Source : Webster's Revised Unabridged Dictionary (1913)

Plod \Plod\, v. i. [imp. & p. p. {Plodded}; p. pr. & vb. n.
   {Plodding}.] [Gf. Gael. plod a clod, a pool; also, to strike
   or pelt with a clod or clods.]
   1. To travel slowly but steadily; to trudge. --Shak.

   2. To toil; to drudge; especially, to study laboriously and
      patiently. ``Plodding schoolmen.'' --Drayton.

Plod \Plod\, v. t.
   To walk on slowly or heavily.

         The ploughman homeward plods his weary way. --Gray.

Source : WordNet®

plod
     v : walk heavily and firmly, as when weary, or through mud;
         "Mules plodded in a circle around a grindstone" [syn: {slog},
          {footslog}, {trudge}, {pad}, {tramp}]
     [also: {plodding}, {plodded}]