prepay

from WordNet (r) 3.0 (2006)

prepay
    v 1: pay for something before receiving it

from The Collaborative International Dictionary of English v.0.48

Prepay \Pre*pay"\, v. t. [imp. & p. p. {Prepaid}; p. pr. & vb.
   n. {Prepaying}.]
   To pay in advance, or beforehand; as, to prepay postage.
   [1913 Webster]