ECHELON

Ech″e‐lon (ĕsh″e‐lŏn), n. [[F., fr. échelle ladder, fr. L. scala.]] 1. 1. (Mil.) An arrangement of a body of troops when its divisions are drawn up in parallel lines each to the right or the left of the one in advance of it, like the steps of a ladder in position for climbing. Also used adjectively; as, echelon distance. Upton (Tactics).
2. 2. (Naval) An arrangement of a fleet in a wedge or V formation. Encyc. Dict.
Echelon lens (Optics), a large lens constructed in several parts or layers, extending in a succession of annular rings beyond the central lens; — used in lighthouses.