DUG is a 3 letter word that starts with D.

1. \Dug\, n. [Akin to Sw. d["a]gga to suckle (a child), Dan.
   d[ae]gge, and prob. to Goth. daddjan. ???.]
   A teat, pap, or nipple; -- formerly that of a human mother,
   now that of a cow or other beast.
   
         With mother's dug between its lips.      --Shak.
   
   

2. \Dug\, imp. & p. p.
   of {Dig}.