1. [n]  religious music used in a procession
2. [adj]  of or relating to or characteristic of a procession; "in good processional order"
3. [adj]  intended for use in a procession; "processional music"; "processional cross"

PROCESSIONAL is a 12 letter word that starts with P.

1. \Pro*ces"sion*al\, a.
   Of or pertaining to a procession; consisting in a procession.
   
         The processional services became more frequent.
                                                  --Milman.
   
   

2. \Pro*ces"sion*al\, n. [F. processionnal, LL.
   processionale.]
   1. (R. C. Ch.) A service book relating to ecclesiastical
      processions. --J. Gregory.
   
   2. A hymn, or other selection, sung during a church
      procession; as, the processional was the 202d hymn.