Source : Webster's Revised Unabridged Dictionary (1913)

Tenderloin \Ten"der*loin`\, n.
   1. A strip of tender flesh on either side of the vertebral
      column under the short ribs, in beef or pork. It consists
      of the psoas muscles.

   2. In New York City, the region which is the center of the
      night life of fashionable amusement, including the
      majority of the theaters, etc., centering on Broadway. The
      term orig. designates the old twenty-ninth police
      precinct, in this region, which afforded the police great
      opportunities for profit through conniving at vice and
      lawbreaking, one captain being reported to have said on
      being transferred there that whereas he had been eating
      chuck steak he would now eat tenderlion. Hence, in some
      other cities, a district largely devoted to night
      amusement, or, sometimes, to vice.

Tenderloin \Ten"der*loin`\, n.
   A strip of tender flesh on either side of the vertebral
   column under the short ribs, in the hind quarter of beef and
   pork. It consists of the psoas muscles.

Source : WordNet®

tenderloin
     n 1: a city district known for its vice and high crime rate [syn:
           {combat zone}]
     2: the tender meat of the loin muscle on each side of the
        vertebral column [syn: {undercut}]