D

D is the fourth (number 4) letter in the alphabet. It comes from the Greek Delta and the Phoenician Dalet.

• In education, D is one letter above a failing grade.
• In electronics, D is a standard size dry cell battery.
• In music, D is a note sometimes called “Re”.
• In Roman numerals, D also means the number 500.
• In computer programming, D is a programming language.

Media related to D at Wikimedia Commons
The dictionary definition of d at Wiktionary