<human>:  Why is the word ‘iridian’ spelled that way?
<bot>: The word iridian is derived from the Greek word <unk> (iris), which means rainbow. In ancient Greek, the word was spelled <i>rydian</i>. The <i>rydian</i> spelling was later changed to <i>iridian</i> because the <i>rydian</i> spelling was considered incorrect.