Source : Webster's Revised Unabridged Dictionary (1913)

Tread \Tread\, v. i. [imp. {Trod}; p. p. {Trodden}, {Trod}; p.
   pr. & vb. n. {Treading}.] [OE. treden, AS. tredan; akin to
   OFries. treda, OS. tredan, D. & LG. treden, G. treten, OHG.
   tretan, Icel. tro?a, Sw. tr[*a]da, tr["a]da, Dan. tr[ae]de,
   Goth. trudan, and perhaps ultimately to F. tramp; cf. Gr. ? a
   running, Skr. dram to run. Cf. {Trade}, {Tramp}, {Trot}.]
   1. To set the foot; to step.

            Where'er you tread, the blushing flowers shall rise.
                                                  --Pope.

            Fools rush in where angels fear to tread. --Pope.

            The hard stone Under our feet, on which we tread and
            go.                                   --Chaucer.

   2. To walk or go; especially, to walk with a stately or a
      cautious step.

            Ye that . . . stately tread, or lowly creep.
                                                  --Milton.

   3. To copulate; said of birds, esp. the males. --Shak.

   {To tread on} or {upon}.
      (a) To trample; to set the foot on in contempt. ``Thou
          shalt tread upon their high places.'' --Deut. xxxiii.
          29.
      (b) to follow closely. ``Year treads on year.''
          --Wordsworth.

   {To tread upon the heels of}, to follow close upon.
      ``Dreadful consequences that tread upon the heels of those
      allowances to sin.'' --Milton.

            One woe doth tread upon another's heel. --Shak.

Tread \Tread\, v. i. [imp. {Trod}; p. p. {Trodden}, {Trod}; p.
   pr. & vb. n. {Treading}.] [OE. treden, AS. tredan; akin to
   OFries. treda, OS. tredan, D. & LG. treden, G. treten, OHG.
   tretan, Icel. tro?a, Sw. tr[*a]da, tr["a]da, Dan. tr[ae]de,
   Goth. trudan, and perhaps ultimately to F. tramp; cf. Gr. ? a
   running, Skr. dram to run. Cf. {Trade}, {Tramp}, {Trot}.]
   1. To set the foot; to step.

            Where'er you tread, the blushing flowers shall rise.
                                                  --Pope.

            Fools rush in where angels fear to tread. --Pope.

            The hard stone Under our feet, on which we tread and
            go.                                   --Chaucer.

   2. To walk or go; especially, to walk with a stately or a
      cautious step.

            Ye that . . . stately tread, or lowly creep.
                                                  --Milton.

   3. To copulate; said of birds, esp. the males. --Shak.

   {To tread on} or {upon}.
      (a) To trample; to set the foot on in contempt. ``Thou
          shalt tread upon their high places.'' --Deut. xxxiii.
          29.
      (b) to follow closely. ``Year treads on year.''
          --Wordsworth.

   {To tread upon the heels of}, to follow close upon.
      ``Dreadful consequences that tread upon the heels of those
      allowances to sin.'' --Milton.

            One woe doth tread upon another's heel. --Shak.

Trod \Trod\,
   imp. & p. p. of {Tread}.

Source : WordNet®

tread
     n 1: a step in walking or running [syn: {pace}, {stride}]
     2: the grooved surface of a pneumatic tire
     3: the part (as of a wheel or shoe) that makes contact with the
        ground
     4: structural member consisting of the horizontal part of a
        stair or step
     [also: {trodden}, {trod}]

tread
     v 1: put down or press the foot, place the foot; "For fools rush
          in where angels fear to tread"; "step on the brake"
          [syn: {step}]
     2: tread or stomp heavily or roughly; "The soldiers trampled
        across the fields" [syn: {trample}]
     3: crush as if by treading on; "tread grapes to make wine"
     4: brace (an archer's bow) by pressing the foot against the
        center
     5: apply (the tread) to a tire
     6: mate with; "male birds tread the females"
     [also: {trodden}, {trod}]

trod
     See {tread}