d d /ˈdiː/

adjective

1. Denoting a quantity consisting of 500 items or units  ( d , five hundred , 500 )
   denoting a quantity consisting of 500 items or units
     The company sold five hundred units of their new product.
   The company sold five hundred units of their new product.
   

 D

noun

1. The 4th letter of the Roman alphabet  ( D )
   the 4th letter of the Roman alphabet
   
2. The cardinal number that is the product of one hundred and five  ( 500 , D , five hundred )
   the cardinal number that is the product of one hundred and five
    The car dealership has over five hundred vehicles for sale
   The car dealership has over five hundred vehicles for sale
   
3. A fat-soluble vitamin that prevents rickets  ( calciferol , cholecalciferol , D , ergocalciferol , viosterol , vitamin D )
   a fat-soluble vitamin that prevents rickets