Source : Webster's Revised Unabridged Dictionary (1913)

Coupon \Cou"pon\ (k??"p?n; F. k??`p?n"), n. [F., fr. couper to
   cut, cut off. See {Coppice}.]
   1. (Com.) A certificate of interest due, printed at the
      bottom of transferable bonds (state, railroad, etc.),
      given for a term of years, designed to be cut off and
      presented for payment when the interest is due; an
      interest warrant.

   2. A section of a ticket, showing the holder to be entitled
      to some specified accomodation or service, as to a passage
      over a designated line of travel, a particular seat in a
      theater, or the like.

Source : WordNet®

coupon
     n 1: a negotiable certificate that can be detached and redeemed
          as needed [syn: {voucher}]
     2: a test sample of some substance