D, as you know, is the 4th letter in the English alphabet. It was also the 4th in the ancient Phoenician, Hebrew, and Greek alphabets. Cool!
But they didn't call their letter D "dee." The Phoenicians and Hebrews called it daleth. The Greeks called it delta. A lot of scholars say the triangle-shaped daleth probably meant a door or archway.
The Greeks built their alphabet from the Phoenicians. To the Greeks, letters were just names for sounds. They kept D when they made their alphabet, but they changed the name from daleth to delta. Delta had three sides that were equal.
When the Romans built their alphabet, they rounded the right part of the triangle and called it de (it's pronoucned day). We use that model of D today.
How Many Sounds
Unlike a lot of other letters, D stands for just one sound, as in donkey. You can also use "ed" for past tense. Therefore, it is pronounced like a T.
In Welsh, when D is doubled (dd), it is pronounced th, as in this.
In Unicode, the capital D is code point U+0044. The lower case D is U+0064.
A Few Meanings for D
*D, on calendars, is normally an abbreviation for December.
*In school terms, D is a barely passing grade.
*D is a standard size dry cell battery.
*In music, D is a note.
*D can also be a vitamin.
*In American Politics, D almost always stands for democrat.