delta

(dĕlˈtə)

noun

1. The fourth letter of the Greek alphabet. See Table at alphabet.
2. An object shaped like a triangle.
3. a. A usually triangular alluvial deposit at the mouth of a river.
   b. A similar deposit at the mouth of a tidal inlet, caused by tidal currents.
4. Mathematics A finite increment in a variable.

Related Forms:

• del·taˈic (-tāˈĭk), delˈtic (-tĭk) adjective

Word History: A Greek letter sits at the mouth of many rivers. Noticing the resemblance between the island formed by sediment at the mouth of a river such as the Nile and the triangular shape of their letter delta (Δ), the Greeks gave the name delta to such an island. English borrowed this sense from Greek, although the word delta appeared first in English as the name of the letter, in a work written possibly around 1200. The sense “alluvial deposit” is not recorded until 1555, when delta is used with reference to the Nile River delta.