Why the Chiaroscuro listing? Em, well, I still believe (probably misguidedly) that Ms. Hambly uses the word in every story (even though she's told me, basically, "Hey, look, it's just a word, stop obsessing over this!"). I cannot completely support my claim, although the following sightings are documented:

First off, in the Windrose Chronicles, chiaroscuro appears:

The Silent Tower: p.115, p.148
The Silicon Mage: p.116, p.192
Dog Wizard: p.116

The p.115/116 trio seemed a little too coincidental for me (but fun). It appears in other books, too:

The Armies of Daylight: p.201
The Magicians of Night: p.309
The Dark Hand of Magic: p.31 (thanks to Lisa Crowe for this one)
The Witches of Wenshar: p. 273 (many thanks to Robin Lloyd for this one - and also for admitting that she could see how an obsession such as this starts!)
Dragonshadow: p.40
Crossroad: p.76 (sent in by Steve Mollmann, much appreciated!)
Bride of the Rat God p.71 (many thanks to Jula Thunert for this sighting!)

Eventually this list expanded, and to date, I have collected:

You, too, can submit a word to the Nifty Word List. The criteria are simple but biased: I have to be unfamiliar with the word and find it aesthetically pleasing.