PLATER is a 6 letter word that starts with P.

1. \Plat"er\, n. (Horse Racing)
   A horse that runs chiefly in plate, esp. selling-plate,
   races; hence, an inferior race horse.
   
   

2. \Plat"er\, n.
   One who plates or coats articles with gold or silver; as, a
   silver plater.
   
   2. A machine for calendering paper.