Delta

Delta, the fourth letter of the Greek alphabet, comes from the Phoenician dalet. In mathematics and science a capital Δ means a change: Δt is a change in time.

River deltas are named after the letter because the Nile’s is roughly triangular. Herodotus is often said to have coined the term, but he only spoke of “the Delta, as it is called by the Ionians”, meaning the Nile’s, and used it for no other river. English began using delta for river mouths in general in the late eighteenth century, in the work of Edward Gibbon.