Source : Webster's Revised Unabridged Dictionary (1913)

Regimental \Reg`i*men"tal\ (-m?n"tal), a.
   Belonging to, or concerning, a regiment; as, regimental
   officers, clothing.

   {Regimental school}, in the British army, a school for the
      instruction of the private soldiers of a regiment, and
      their children, in the rudimentary branches of education.

Source : WordNet®

regimental
     adj : belonging to or concerning a regiment; "regimental units"