1. [adj]  of or relating to the iris of the eye
2. [adj]  of or containing iridium

IRIDIC is a 6 letter word that starts with I.

1. \I*rid"ic\, a.
   Of or pertaining to the iris of the eye.
   
   

2. \I*rid"ic\, a. (Chem.)
   Of or pertaining to iridium; -- said specifically of those
   compounds in which iridium has a relatively high valence.