- fourth letter of the Latin alphabet, third consonant
- phonetic name: "voiced alveolar plosive"; sound: place your tongue under your alveolar ridge and make a percussive breath of air as your release your tongue
- in Egyptian, three hieroglyphs pronounced similar to 'D': a hand, a loaf of bread, and a cobra
- in Phoenician/Hebrew, the equivalent was daleth, which can be interpreted as a door, a breast, or a fish
- adopted by Greeks as delta: Δ (upper case), δ (lower case)
- in Roman, 'D' represents 500
- 'D' in grade school stands for "unsatisfactory"
- in business, delta has become associated "elite" (ie. Delta Airlines)
- Russian equivalent is de (Д)
- with a numeric value of 4, it is also associated with a square and can represent matter
- common sets of 4 bring us closer to reality: 4 cardinal points (north, south, east, west), 4 elements (earth, water, wind, fire) and 4 seasons (spring, summer, fall, winter)
- 'D' in music is the note "re", the second note in a C-major musical scale; "re" is associated with the second chakra, considered is a central point which radiates energy throughout the body, and is also tied to the colour orange and element water
- associated with passages, becoming
- 'D' in chemistry stands for vitriol (former name for ferrous sulphate or copper sulphate)
- 'D' in biology is asparate, an amino acid
- 'D' in crossword puzzles stands for Down
- in American politics, D is often used as an abbreviation for a Democrat
- D can also abbreviate dam, date, daughter, day, degree, delete, department, diameter, died, director, dollar, Don, dose, Dutch, duchess, duke, Germany
- NATO phonetic alphabet: DELTA
- Vitamin D (in forms D2 or D3) are essential for the absorption of calcium which promotes bone strength. It can be obtained from sunlight, liver, eggs, and fish oils.
- in war, dead bodies sometimes have the letter 'D' marked on their forehead
- in military, "D-Day" refers to the initiation of a combat operation; the most famous would be the Normandy Invasion on June 6th, 1944
