The Collaborative International Dictionary of English v.0.48:

Prolongation \Pro`lon*ga"tion\, n. [F. prolongation.]
   [1913 Webster]
   1. The act of lengthening in space or in time; extension;
      protraction. --Bacon.
      [1913 Webster]

   2. That which forms an additional length.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prolongation
    n 1: the act of prolonging something; "there was an indefinite
         prolongation of the peace talks" [syn: prolongation,
         protraction, perpetuation, lengthening]
    2: amount or degree or range to which something extends; "the
       wire has an extension of 50 feet" [syn: extension,
       lengthiness, prolongation]
    3: the consequence of being lengthened in duration [syn:
       lengthiness, prolongation, continuation, protraction]