DELF is a 4 letter word that starts with D.

1. \Delf\, n. [AS. delf a delving, digging. See {Delve}.]
   A mine; a quarry; a pit dug; a ditch. [Written also {delft},
   and {delve}.] [Obs.]
   
         The delfts would be so flown with waters, that no gins
         or machines could . . . keep them dry.   --Ray.
   
   

2. \Delf\, n.
   Same as {Delftware}.