1911 Encyclopædia Britannica/Defile
DEFILE, a military expression for a passage, to march through which troops are compelled to “defile,” or narrow their front (from the Fr. défiler, to march in a line, or by “files”). The word is usually applied to a ravine or gorge in a range of hills, but a causeway over a river, a bridge and even a village may equally be called a defile. The term is also used to express, without any special reference to military operations, a gorge in mountains. The verb “to defile” is used of troops marching on a narrow front, or narrowing their front, under all circumstances, and in this sense is the contrary of “deploy.”
“Defile,” in the sense of “pollute,” is another form of “defoul”; though spelt alike, the two words are pronounced differently, the accent being on the first syllable for the former and on the second for the latter.