DEFILE, a military expression for a passage, to march through which troops are compelled to "defile," or narrow their front (from the Fr. defiler, 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.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)