The Collaborative International Dictionary of English v.0.48:

Bottomry \Bot"tom*ry\, n. [From 1st Bottom in sense 8: cf. D.
   bodemerij. Cf. Bummery.] (Mar. Law)
   A contract in the nature of a mortgage, by which the owner of
   a ship, or the master as his agent, hypothecates and binds
   the ship (and sometimes the accruing freight) as security for
   the repayment of money advanced or lent for the use of the
   ship, if she terminates her voyage successfully. If the ship
   is lost by perils of the sea, the lender loses the money; but
   if the ship arrives safe, he is to receive the money lent,
   with the interest or premium stipulated, although it may, and
   usually does, exceed the legal rate of interest. See
   Hypothecation.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

BOTTOMRY, maritime law. A contract, in nature of a mortgage of a ship, on
which the owner borrows money to enable him to fit out the ship, or to
purchase a cargo, for a voyage proposed: and he pledges the keel or bottom
of the ship, pars pro toto, as a security for the repayment; and it is
stipulated that if the ship should be lost in the course of the voyage, by
any of the perils enumerated in the contract, the lender also shall lose his
money but if the ship should arrive in safety, then he shall receive back
his principal, and also the interest agreed upon, which is generally called
marine interest, however this may exceed the legal rate of interest. Not
only the ship and tackle, if they arrive safe, but also the person of the
borrower, is liable for the money lent and the marine interest. See 2 Bl.
Com. 458; Marsh. Ins. B. 21 c. 1; Ord. Louis XIV. B. 3, tit. 5; Laws of
Wishuy, art. 45 Code de Com. B. 2, tit. 9.
     2. The contract of bottomry should specify the principal lent, and the
rate of marine interest agreed upon; the subject on which the loan is
effected the names of the vessel and of the master those of the lender and
borrower whether the loan be for an entire voyage; for what voyage and for
what space of time; and the period of re-payment. Code de Com. art. 311
Marsh. Ins. B. 2.
     3. Bottomry differs materially from a simple loan. In a loan, the money
is at the risk of the borrower, and must be paid at all events. But in
bottomry, the money is at the risk of the lender during the voyage. Upon a
loan, only legal interest can be received; but upon bottomry, any interest
may be legally reserved which the parties agree upon. See, generally, Metc.
& Perk. Dig. h. t.; Marsh. Inst. B. 2; Bac. Abr. Merchant, K; Com. Dig.
Merchant. E 4; 3 Mass. 443; 8 Mass. 340; 4 Binn. 244; 4 Cranch, 328; 3 John.
R. 352 2 Johns. Cas. 250; 1 Binn. 405; 8 Cranch, 41 8; 1 Wheat. 96; 2 Dall.
194. See also this Dict. tit. Respondentia; Vin. Abr. Bottomry Bonds 1 Bouv.
Inst. n. 1246-57.