The Collaborative International Dictionary of English v.0.48:

Lutetium \Lu*te"ti*um\, n. (Chem.)
   A metallic element separated from ytterbium in 1907, by
   Urbain in Paris and by von Welsbach in Vienna. It is a member
   of the Lanthanide rare earth group. Symbol, Lu; atomic number
   71; atomic weight 174.967 [C=12.011]. Previously spelled
   Lutecium.
   [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

lutetium
    n 1: a trivalent metallic element of the rare earth group;
         usually occurs in association with yttrium [syn:
         lutetium, lutecium, Lu, atomic number 71]

The Elements (07Nov00):

lutetium
Symbol: Lu
Atomic number: 71
Atomic weight: 194.967
Silvery-white rare-earth metal which is relatively stable in air. It
happens to be the most expensive rare-earth metal. Its found with almost
all rare-earth metals, but is very difficult to separate from other
elements. Least abundant of all natural elements. Used in metal alloys,
and as a catalyst in various processes. There are two natural, stable
isotopes, and seven radioisotopes, the most stable being Lu-174 with a
half-life of 3.3 years. The separation of lutetium from ytterbium was
described by Georges Urbain in 1907. It was discovered at approximately
the same time by Carl Auer von Welsbach. The name comes from the Greek
word lutetia which means Paris.