Meaning of D in English

D BrE AmE , d /diː/ ( plural D’s , d’s ) noun

1 . [uncountable and countable] the fourth letter of the English alphabet

2 . [uncountable and countable] the second note in the musical ↑ scale of C ↑ major or the musical ↑ key based on this note

3 . [countable] a mark given to a student’s work to show that it is not very good:

I got a D in history last semester.

4 . the number 500 in the system of ↑ roman numeral s

⇨ ↑ D and C

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.