The Collaborative International Dictionary of English v.0.48:
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[aum]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.
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
Ye that . . . stately tread, or lowly creep.
3. To copulate; said of birds, esp. the males. --Shak.
To tread on or To tread upon.
(a) To trample; to set the foot on in contempt. "Thou
shalt tread upon their high places." --Deut. xxxiii.
(b) to follow closely. "Year treads on year."
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.