The Collaborative International Dictionary of English v.0.48:

rofecoxib \rofecoxib\ (Chem. & Med.)
   A chemical substance (C17H14O4S, molecular weight 314.36)
   used in medicine as an analgesic to alleviate pain and
   inflammation; it is a synthetic compound, and is marketed by
   Merck & Co. under the trade name Vioxx, in tablets giving
   dosages of 12.5 or 25 milligrams. It is classed as a
   non-steroidal anti-inflammatory drug (NSAID). Chemically, it
   is 4-[4-(methylsulfony)phenyl]-3-phenyl-2(5H) furanone. Its
   chemical structure contains two phenyl rings and a furanone
   ring. It is believed to act by inhibition of prostaglandin
   biosynthesis, through inhibition of the enzyme
   cyclooxygenase-2 (COX-2); unlike aspirin, it does not
   inhibit cyclooxygenase-1.
   [PJC]

WordNet (r) 3.0 (2006):

rofecoxib
    n 1: a Cox-2 inhibitor (trade name Vioxx) that relieves pain and
         inflammation without harming the digestive tract;
         voluntarily withdrawn from the market in 2004 [syn:
         rofecoxib, Vioxx]