Pulmonary embolism. Pulmonary embolism Pulmonary embolism occurs when a blood clot gets lodged in an artery in the lung, blocking blood flow to part of the lung. Blood clots most often originate in the legs and travel up through the right side of the heart and into the lungs.
WordReference Random House Unabridged Dictionary of American English Â© 2016. tread (tred), v., trod, trodâ¢den ortrod, treadâ¢ing, n. v.i. 1  to set down the foot or feet in walking; step; walk.  to step, walk, or trample so as to press, crush, or injure something (usually fol. by on or upon):to tread on a person's foot.
Today most tires are pneumatic tires, though typically still referred to as just tires. The word pneumatic simply means an item that uses air. Tires work because they have tread on them. Tread is the raised patterns that appear on the top of a new tire, which often appear to zigzag around the tire. The tread helps the tire gain traction on the road to prevent it from sliding.