The Collaborative International Dictionary of English v.0.48:

Regimental \Reg`i*men"tal\ (-m[e^]n"tal), a.
   Belonging to, or concerning, a regiment; as, regimental
   officers, clothing.
   [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

regimental
    adj 1: belonging to or concerning a regiment; "regimental units"