The Collaborative International Dictionary of English v.0.48:

Quintuple \Quin"tu*ple\, v. t. [imp. & p. p. Quintupled; p.
   pr. & vb. n. Quintupling.] [Cf. F. quintupler.]
   To make fivefold, or five times as much or many.
   [1913 Webster]

WordNet (r) 3.0 (2006):

quintupling
    n 1: increasing by a factor of five