The Collaborative International Dictionary of English v.0.48:

Loin \Loin\, n. [OE. loine, OF. logne, F. longe, from (assumed)
   LL. lumbea, L. lumbus join. Cf. Lends, Lumbar,
   Nombles.]
   1. That part of a human being or quadruped, which extends on
      either side of the spinal column between the hip bone and
      the false ribs. In human beings the loins are also called
      the reins. See Illust. of Beef.
      [1913 Webster]

   2. A cut of meat taken from this part of a food animal, as
      from cattle or hogs.
      [PJC]

   3. pl. The pubic area; the genitalia, especially in women;
      as, receptive loins.
      [PJC]

WordNet (r) 3.0 (2006):

loin
    n 1: a cut of meat taken from the side and back of an animal
         between the ribs and the rump
    2: either side of the backbone between the hipbone and the ribs
       in humans as well as quadrupeds [syn: loin, lumbus]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "loin":
   Chateaubriand, back, blade roast, breast, brisket, chuck,
   chuck roast, clod, cold cuts, dorsal region, dorsum, filet mignon,
   flank, knuckle, plate, plate piece, pot roast, rack, rib roast,
   ribs, ridge, roast, rolled roast, round, rump, rump roast, saddle,
   shank, short ribs, shoulder, shoulder clod, sirloin, tenderloin