Fantasy
Illusion
noun, の adjective
An illusion that you imagine is your big fantasy (it's also an illusion). This makes sense, though, right? An illusion is an illusion, sure. But, when you imagine it, it becomes your fantasy!
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
それは幻想です。
That is an illusion.
秋の京都の夜って、とても幻想的なんですよ。
Kyoto nights in autumn are very magical.
会場の雰囲気がステキすぎて、まるで幻想の世界にいるような気分になりました。
The atmosphere of the venue was so beautiful that I felt like I was in a fantasy world.