Sentence:  A horse is <WSD>roughshod</WSD> when the nails are left protruding out of its shoes so that the animal does not slip and fall. Consequently, being ridden over by a <WSD>roughshod</WSD> horse would be quite agonizing. 
Meaning of the word marked with <WSD> tags:  Of a horse: having hooves shod with calks or horseshoes that have projecting nails to prevent slipping.