The Collaborative International Dictionary of English v.0.48:

Nicene \Ni"cene\, a. [L. Nicaenus, fr. Nicaea Nice, Gr. ?.]
   Of or pertaining to Nice, a town of Asia Minor, or to the
   ecumenical council held there a. d. 325.
   [1913 Webster]

   Nicene Creed, a summary of Christian faith, composed and
      adopted by the Council of Nice, against Arianism, a. d.
      325, altered and confirmed by the Council of
      Constantinople, a. d. 381, and by subsequent councils.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Nicene
    adj 1: of or relating to the ancient city of Nicaea in Asia
           Minor [syn: Nicaean, Nicene]