The Collaborative International Dictionary of English v.0.48:

Prolongate \Pro*lon"gate\, v. t. [imp. & p. p. Prolongated; p.
   pr. & vb. n. Prolongating.] [L. prolongatus, p. p. of
   prolongare. See Prolong.]
   To prolong; to extend in space or in time. [R.]
   [1913 Webster]