fan·ta·sy (fanÆtà s", -z"), n., pl. -sies, v., -sied, -sy·ing.

–n.
1.    imagination, esp. when extravagant and unrestrained.
2.    the forming of mental images, esp. wondrous or strange fancies; imaginative conceptualizing.
3.    a mental image, esp. when unreal or fantastic; vision: a nightmare fantasy.
4.    Psychol. an imagined or conjured up sequence fulfilling a psychological need; daydream.
5.    a hallucination.
6.    a supposition based on no solid foundation; visionary idea; illusion: dreams of Utopias and similar fantasies.
7.    caprice; whim.
8.    an ingenious or fanciful thought, design, or invention.
9.    Also, fantasia. Literature. an imaginative or fanciful work, esp. one dealing with supernatural or unnatural events or characters: The stories of Poe are fantasies of horror.
10.    Music. fantasia (def. 1).
–v.t., v.i.
11.    to form mental images; imagine; fantasize.
12.    Rare. to write or play fantasias.
Also, phantasy.
[1275–1325; ME fantasie imaginative faculty, mental image (< AF, OF) < L phantasia < Gk phantas#a an idea, notion, image, lit., a making visible; see FANTASTIC, -Y3]