tread

For the verb: "to tread"

Simple Past:	trod
Past Participle:	trodden

Multiple Entries:
  tread    caterpillar  

Concise Oxford English Dictionary © 2008 Oxford University Press:
tread/tred/

▶verb (past trod; past part. trodden or trod)

• 1 walk in a specified way.

  ■ (tread on) chiefly Brit. set one's foot down on top of.

  ■ walk on or along.

• 2 press down or crush with the feet.

▶noun

• 1 a manner or the sound of walking.

• 2 (also tread board) the top surface of a step or stair.

• 3 the thick moulded part of a vehicle tyre that grips the road.

  ■ the part of a wheel that touches the ground or rail.

• 4 the part of the sole of a shoe that rests on the ground.

• 5 the upper surface of a railway track, in contact with the wheels.

– phrases
tread (or chiefly N. Amer. step) on someone's toes offend someone by encroaching on their area of responsibility.
tread water

• 1 maintain an upright position in deep water by moving the feet with a walking movement and the hands with a downward circular motion.

• 2 fail to make progress.

– derivatives
treader noun.

– origin OE tredan, of W. Gmc origin.

Concise Oxford English Dictionary © 2008 Oxford University Press:
caterpillar/ˈkatəpɪlə(r)/

▶noun

• 1 the larva of a butterfly or moth.

• 2 (also caterpillar track or tread) trademark an articulated steel band passing round the wheels of a vehicle for travel on rough ground.

– origin ME: perh. from a var. of OFr. chatepelose, lit. ‘hairy cat’, influenced by obs. piller ‘ravager’.