Sentence:  We were less than a quarter of a mile from the road , and we could trace its shape from the ribbon of <WSD>powder</WSD> smoke and dust that hung over it . 
Meaning of the word marked with <WSD> tags:  a mixture of potassium nitrate, charcoal, and sulfur in a 75:15:10 ratio which is used in gunnery, time fuses, and fireworks