The Collaborative International Dictionary of English v.0.48:

Durative \Dur"a*tive\, a.
   Continuing; not completed; implying duration.
   [1913 Webster]

         Its durative tense, which expresses the thought of it
         as going on.                             --J. Byrne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

durative
    n 1: the aspect of a verb that expresses its duration [syn:
         durative, durative aspect]