tread 
(trĕd)
(trĕd)v. trod (trŏd) or treaded, trod·den (trŏdn) or trod or treaded, tread·ing, treads
v.tr.
1. To walk on, over, or along: tread the pavement.
2. To press beneath the feet; trample: dirt that was trodden into the rug.
3. To treat unjustly or harshly; oppress: people who were trodden down by tyrants.
4. To form by walking or trampling: tread a path.
5. To execute by walking or dancing: tread a measure.
6. To copulate with. Used of a male bird.
v.intr.
1.
a. To go on foot; walk.
b. To set down the foot; step.
2.
a. To trample something. Used with on or upon: Don't tread on the new grass.
b. To treat someone or something unjustly or harshly. Used with on or upon: a regime treading upon the rights of the citizens.
3. To copulate. Used of birds.
n.
Idioms: 1.
a. The act, manner, or sound of treading.
b. An instance of treading; a step.
c. A mark made by treading, as in snow.
2. The upper horizontal part of a step in a staircase.
3.
a. The part of a wheel or tire that makes contact with the road or rails.
b. The grooved face of a tire.
4. The part of a shoe sole that touches the ground.
5. Either of the continuous ridged belts with which bulldozers, tanks, and certain other vehicles move over the ground.
tread the boards
To act on the stage: "We who tread the boards are not the only players of parts in this world" (John Fowles).
tread water
1. To keep the head above water while in an upright position by pumping the legs.
2. To expend effort but make little or no progress to achievement of a goal or an end.
[Middle English treden, from Old English tredan.]
treadless adj.