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.
Definition of tread. 1  1a (1) : the part of a wheel or tire that makes contact with a road or rail (2) : the pattern of ridges or grooves made or cut in the face of a tireb : the part of a shoe or boot sole that touches the ground; also : the pattern on the bottom of a sole. 2  2a : the upper horizontal part of a stepb : the width of such a tread.