The Collaborative International Dictionary of English v.0.48:

Ir \Ir\ n. (Chem.)
   The chemical symbol for iridium, a metallic element of the
   platinum group. It has atomic number 77 and an atomic weight
   of 192.22.

   Syn: iridium.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Ir- \Ir-\
   A form of the prefix in-. See In-.
   [1913 Webster]