The Collaborative International Dictionary of English v.0.48:

Hypothecate \Hy*poth"e*cate\, v. t. [imp. & p. p.
   Hypothecated; p. pr. & vb. n. Hypothecating.] [LL.
   hypothecatus, p. p. of hypothecare to pledge, fr. L.
   hypotheca pledge, security. See Hypotheca.] (Law)
   To subject, as property, to liability for a debt or
   engagement without delivery of possession or transfer of
   title; to pledge without delivery of possession; to mortgage,
   as ships, or other personal property; to make a contract by
   bottomry. See Hypothecation, Bottomry.
   [1913 Webster]

         He had found the treasury empty and the pay of the navy
         in arrear. He had no power to hypothecate any part of
         the public revenue. Those who lent him money lent it on
         no security but his bare word.           --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hypothecate
    v 1: pledge without delivery or title of possession
    2: to believe especially on uncertain or tentative grounds;
       "Scientists supposed that large dinosaurs lived in swamps"
       [syn: speculate, theorize, theorise, conjecture,
       hypothesize, hypothesise, hypothecate, suppose]