1》 the fourth letter of the Greek alphabet ( Δ , δ ), transliterated as ‘d’.
↘[as modifier ] denoting the fourth in a series of items or categories.
↘ Brit. a fourth-class mark given for a piece of work.
2》 a code word representing the letter D, used in radio communication.
■ symbol Mathematics variation of a variable or quantity.
Gk, from Phoenician daleth .
■ noun a triangular tract of sediment deposited at the mouth of a river, typically where it diverges into several outlets.
C16: orig. the Delta (of the River Nile), from the shape of the Gk letter (see ~ 1 ).