Sentence:  A man dressed as a lab tech, his blue scrubs startlingly pale against the vivid red and black chaos, moved into sight from behind the SUV. He carried an <WSD>assault rifle</WSD>. 
Meaning of the word marked with <WSD> tags:  A military select-fire rifle or carbine that fires a shortened rifle caliber round or lower-power smaller-calibre round, from a high-capacity magazine.