Which word is used to represent the letter D?

The term used to represent the letter D in the phonetic alphabet is "Delta." The phonetic alphabet is designed to provide a clear and concise way to communicate letters over radio or telephone, particularly in situations where clarity is crucial, such as in military communication, aviation, and other fields.

"Delta" is part of the NATO phonetic alphabet, which was adopted by various organizations, including the military, to ensure that letters are distinctly understood, especially in noisy environments or when speaking across communication devices. Each letter is associated with a specific word to eliminate confusion — for example, "B" is represented by "Bravo," "C" by "Charlie," and so forth.

Other terms like "Dove," "Doc," and "Dart" are not part of the phonetic alphabet and do not serve a standardized role in denoting the letter D. Therefore, "Delta" is the correct word to represent that letter.