imagination 含义广，一般不含贬义。可指认真、带有启发性的想象，也可指凭记忆的想象或凭空想象事物的能力。
fancy 指脱离实际的幻想或幻想力，常暗含所想象的东西近乎怪诞的意味。
fantasy 指与现实完全脱节，荒诞离谱、稀奇古怪的想象。
参考例句
1. Imagination, life is your creation. 想象生活是你创造的。
2. All in all, are not of the imagination. 一切的一切，都不是想象中的了。
3. Imagination is a creative power that is necessary for inventing a new machine. 想象力是一种创造的力量即必然的发明一些新的机器。
英英解释
n.
1. the formation of a mental image of something that is not perceived as real and is not present to the
2. the ability to form mental images of things or events
3. the ability to deal resourcefully with unusual problems
