1. [n]  a regulated daily food allowance
2. [adj]  of or relating to the diet; "dietary restrictions"

DIETARY is a 7 letter word that starts with D.

1. \Di"et*a*ry\, a.
   Pertaining to diet, or to the rules of diet.
   
   

2. \Di"et*a*ry\, n.; pl. {Dietaries}.
   A rule of diet; a fixed allowance of food, as in workhouse,
   prison, etc.