How do you describe a pearl? It doesn't shine like other gems. Doesn't shimmer, has no fire. It gleams, yes. But it's the rainbow of color that really sets it apart. That . . . you know, the pearlized effect. ;-) Its iridescence.
I can never think of a more accurate word for it, so I was a little frustrated when I looked up "iridescent" and realized it entered English just a wee bit too late for my 1780 book. As in, 16 years later, in 1796. After grumbling for a minute over not being able to justify using it (I'm nit-picky about my word choices like that), I put it aside to wonder about the word.
"Iridescent" comes from the word "iris." Now, we all know "iris," right? The colored part of our eyes. A flower. Yep. But apparently "iris" means rainbow in Greek--hence why the colored part of our eyes are called that. The Greeks would also use it to describe any colored circle, like the round "eyes" on a peacock feather. Pretty neat, huh?
So it makes perfect sense that we would have created a word like "iridescent" to describe that rainbow effect. If only we had created it two decades earlier . . . ;-)
(Photo credited to Georg Oleschinski/Inst. f. Paläont., Uni Bonn via Wikipedia Commons)