*delta*

n.; pl. Deltas [ Gr. de`lta, the name of the fourth letter of the Greek alphabet (the capital form of which is Δ, Eng. D), from the Phœnician name of the corresponding letter. The Greeks called the alluvial deposit at the mouth of the Nile, from its shape, the Delta of the Nile. ] 1. The fourth letter of the Greek alphabet (Δ δ), corresponding to D. Hence, an object having the shape of the capital Δ. [ Webster 1913 Suppl. ]

2. A tract of land shaped like the letter delta (Δ), especially when the land is alluvial and inclosed between two or more mouths of a river; as, the delta of the Ganges, of the Nile, or of the Mississippi. [ 1913 Webster ]

3. (Elec.) The closed figure produced by connecting three coils or circuits successively, end for end, esp. in a three-phase system; -- often used attributively, as delta winding, delta connection (which see), etc. [ Webster 1913 Suppl. ]