【Imaginary】 ,  【fanciful】 ,  【visionary】 ,  【fantastic】 ,  【chimerical】 ,  【quixotic】  are comparable when they are applied to conceptions or to the persons who form the conceptions and mean unreal or unbelievable and out of keeping with things as they are or conceiving such unreal or unbelievable things.

Something is  【imaginary】 which is fictitious and purely the product of an active or an excited imagination.

Something is or, less often, one is  【fanciful】 which or who indicates a giving rein to the power of conceiving or producing things that have no real counterpart in nature or in fact.

Something is 【visionary】 which, although it seems real and practical to the one who conceives it, is usually the product of a dream or vision or of an unrestrained imagination and is incapable of realization.

One is  【visionary】 who is given to such dreams, visions, and fancies and inspired by the hopes they arouse.

Something is  【fantastic】  (see also  【FANTASTIC】 2 ) which is or, more often, seems extravagantly 【fanciful】 or queer and hence incapable of belief or, sometimes, approval.

Something is  【chimerical】 which is wildly or fantastically 【visionary】 or unreal.

Something is or one is  【quixotic】 which or who is motivated by extravagantly chivalrous devotion to 【visionary】 ideals.