Chaosiums "King Arthur Pendragon" .. around 1980 or something.
And they "borrowed" it, too, since it is the "historically correct term".
Actually, this sidhe/fay/fomorian ability is more than mere illusion, it's something about altering reality, or switching reality (they're all from some "otherworld", after all)
E.G.:
You meet some nice folks on a clearing.
You sit down with them and have a meal 'til late in the evening, lets say some really gorgous looking, smelling, tasting bread.
After that, you fell asleep.
Upon awakening the next morning, you find out that the strange folk is gone .. and that the bread has turned into stone - again.
Obviously, you wouldn't have been able eat stone, even if it looked like bread. So, under
glamour, it must have had different pyhsical properties.
Another example:
There's a story about Merlin marching Kin Ban's army over 165 miles within two or three days, supposedly through some misty "otherworld" what shortened the length of path considerably.
Mmmmhhmm .. thinking about it - today's use of the word doesn't seem to be to much "off" - it's just that most people do not understand it anymore:
Glamour still is an enchantment/bewitchment which changes the laws of physics and logics in a limited place for limited time, beyond the comprehension of mere mortals, isn't it?