/del"teuh/ , n.
1. the fourth letter of the Greek alphabet.
2. the consonant sound represented by this letter.
3. the fourth in a series of items.
4. anything triangular, like the Greek capital delta.
5. Math. an incremental change in a variable.
6. a nearly flat plain of alluvial deposit between diverging branches of the mouth of a river, often, though not necessarily, triangular: the Nile delta.
7. ( usually cap. ) a word used in communications to represent the letter D.
8. ( cap. ) Astron. a star that is usually the fourth brightest of a constellation: The fourth brightest star in the Southern Cross is Delta Crucis.
[ 1350-1400; ME deltha delta délta; akin to Heb daleth ]