The Collaborative International Dictionary of English v.0.48:

Kantian \Kant"i*an\, a.
   Of or pertaining to Immanuel Kant, the German philosopher;
   conformed or relating to any or all of the philosophical
   doctrines of Immanuel Kant.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Kantian \Kant"i*an\, n.
   A follower of Kant; a Kantist. Kantianism

WordNet (r) 3.0 (2006):

Kantian
    adj 1: of or relating to Immanuel Kant or his philosophy