Bonds made payable to bearer had certificates of interest, which could be cut from the bond and presented for payment. These pieces of paper cut off are the bonds coupons.  Coupon bonds had coupons.
An unregistered, negotiable, bearer bonds on which interest and principal are payable to the holder, regardless of whom it was originally issued to. The coupons are attached to the bond, and each coupon represents a single interest payment. The holder submits a coupon, usually semi-annually, to the issuer or paying agent to receive payment. Coupon bonds are being phased out in favor of registered bonds. 
Bond 13c anything that binds, householder, dweller. Legalistic sense first recorded 1590s.  Bondage c.1300, "condition of a serf or slave, a serf, tenant farmer, householder, dwell, prepare, inhabit, to be, exist, dwell. The sexual sado-masochism sense is recorded by 1966.  Coupon from 1822, "certificate of interest due on a bond"  Denoting a detachable portion of a bond to be given up in return for payment of interest: from French, literally ‘piece cut off,’ from couper ‘cut.’