The grammatical sense is attested in English from late 14c. The form is thought to derive from an early pictograph, possibly Egyptian, indicating the folding door of a tent. , pl. D, d (di) n. D, or d, is the fourth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. D-BAT Lakeside is the Premier Baseball and Softball training facility in the country. Informal. It corresponds to Semitic daleth and Greek delta (Δ). any spoken sound represented by this letter. This super-catchy and clear alphabet song also lets children hear the letter D sound and see each letter at the beginning of five simple words paired with colorful kid-friend images.