WordNet (r) 3.0 (2006):

rhenium
    n 1: a rare heavy polyvalent metallic element that resembles
         manganese chemically and is used in some alloys; is
         obtained as a by-product in refining molybdenum [syn:
         rhenium, Re, atomic number 75]

The Elements (07Nov00):

rhenium
Symbol: Re
Atomic number: 75
Atomic weight: 186.2
Silvery-white metallic transition element. Obtained as a by-product of
molybdenum refinement. Rhenium-molybdenum alloys are superconducting.