From Ancient Greek δέλτα (délta), borrowed from a Phoenician word for "door", ultimately from Proto-Semitic *dalt-. Doublet of dalet.
* (river): from the triangular shape of the majuscule Greek letter delta Δ
* (USSF): from the delta wing, symbol of the USSF, a triangular wing, shaped like the majuscule Greek letter delta Δ