1 Having a changeable luster like that of a cat's eye at night.
2 (of a gem, especially when cut en cabochon) showing a band of bright lustre caused by reflection from inclusions in the stone.
It is a chatoyant stone meaning that it shows bands of bright reflected light and gives off a silky luster with a 'cat's eye' effect. (Tiger Eye, Crystal Council)
She invariably wore gloves out of doors and a veil to conceal the chatoyant eyes. (Sax Rohmer, The Green Eyes of Bast )
The chatoyant eyes of the leopard stared back, a flicker of restlessness in their brilliant yellow deeps. The tip of the tail twitched. (Harold MacGrath, The Adventures of Kathlyn )
His eyes rested on a naturalistic drawing of Lori, smiling her chatoyant smile. (Charles McGarry, The Last Supper)
Though we might define this word in general to refer to something having a changeable, varying lustre or colour, no two dictionaries entirely agree on its current application. Some mention only the bright lustre of a gem caused by reflections from within the stone, since the word now most often appears in discussions by gemologists; but other dictionaries mention the sheen of a bird's plumage or the changing colours and texture of a material such as silk.
All agree, however, that the source of the concept is the gleam of a cat's eyes in the dark. The source is the eighteenth-century French verb chatoyer, to shine like a cat's eyes (based on chat, French for cat). Its French connections remain so strong that it is still sometimes said as though it were a French word.
Many examples in English literature refer to shining eyes, as in The Insidious Dr Fu-Manchu, by Sax Rohmer, of 1913: "I managed to move sufficiently to see at the top, as I fired up the stairs, the yellow face of Dr Fu-Manchu, to see the gleaming, chatoyant eyes, greenly terrible, as they sought to pierce the gloom." (World Wide Words)
The complex structure of a cat's eye not only enables it to see at night but also gives it the appearance of glowing in the dark. Not surprisingly, jewels that sport a healthy luster are often compared with the feline ocular organ, so much that the term cat's-eye is used to refer to those gems (such as chalcedony) that give off iridescence from within. If you've brushed up on your French lately, you might notice that the French word for cat (chat) provides the first four letters of chatoyant, a word used by jewelers to describe such lustrous gems (and by others who see the same luster elsewhere). Chatoyant derives from the present participle of chatoyer, a French verb that literally means "to shine like a cat's eyes." (Merriam-Webster)