delta1

noun

• 1the fourth letter of the Greek alphabet (Δ, δ), transliterated as ‘d’.
• British a fourth-class mark given for an essay, examination paper, or other piece of work.
• [as modifier] the fourth in a series of items, categories, etc.:delta hepatitis
• (Delta) [followed by Latin genitive] Astronomy the fourth (usually fourth-brightest) star in a constellation:Delta Cephei

• 2a code word representing the letter D, used in radio communication.

• 3 (also delta connection) a triangular arrangement of electrical three-phase windings.

symbol

• (δ) Mathematics variation of a variable or function.
• (Δ) Mathematics a finite increment.
• (δ) Astronomy declination.