Chatoyant \shuh-TOI-uhnt\ , adjective;
1. Having changeable lustre; twinkling
2. (Of a gem, especially a cabochon) displaying a band of light reflected off inclusions of other minerals
This word is first attested in 1798 and comes from French chatoyant, which conveys the same sense in French as it does in English. The OED also references a Latin word caticā-re, but I can't figure out what they are talking about. Lexicographer Émile Littré defined one entry of chatoyer as "to stroke or caress as a cat, to pet." It's worth mentioning here that chat is the French word for cat, but I doubt chatoyer is derived from chat in any way.
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Thursday, January 6
Etymologies come from the Oxford English Dictionary and/or Etymonline.com