@James34,
I think James is correct.
Quick definitions from Macmillan (trod)
▸ noun: structural member consisting of the horizontal part of a stair or step
▸ noun: the part (as of a wheel or shoe) that makes contact with the ground
▸ noun: the grooved surface of a pneumatic tire
▸ noun: a step in walking or running
▸ verb: apply (the tread) to a tire
▸ verb: brace (an archer's bow) by pressing the foot against the center
▸ verb: mate with ("Male birds tread the females")
▸ verb: crush as if by treading on ("Tread grapes to make wine")
▸ verb: tread or stomp heavily or roughly
▸ verb: put down or press the foot, place the foot ("For fools rush in where angels fear to tread")
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▸ Also see tread