【Fancy】 ,  【fantasy】 ,  【phantasy】 ,  【phantasm】 ,  【vision】 ,  【dream】 ,  【daydream】 ,  【nightmare】  are comparable when they denote a vivid idea or image, or a series of such ideas or images, present in the mind but having no concrete or objective reality.

【Fancy】 (see also IMAGINATION ) is applicable to anything which is conceived by the imagination, whether it recombines the elements of reality or is pure invention.

【Fantasy】 applies to a 【fancy】 and especially to an organized series of fancies (as one presented in art) that is the product of an unrestrained imagination freed from the bonds of actuality.

【Phantasy】 , though sometimes used in place of  【fantasy】 , both as the power of free inventive imagination and as a product of that power, may apply particularly to the image-making power of the mind, whether the image is the result of sense perception or of the imagination, or to a product of that power and then may be strongly antonymous to truth and reality.

【Phantasm】 may be applied either to a 【phantasy】 , the mental image or to a 【fantasy】 , especially to one that is hallucinatory.

【Vision】  often implies an imagining, but it as frequently implies a seeing or a revelation. Specifically, however, the term is applied to something which the mind perceives as clearly or concretely as if revealed to it by a supernatural or mysterious power (see REVELATION ), or as if viewed by a kind of spiritual sight or intuition, or as if seen in a 【dream】 ;  【vision】 therefore often suggests a sight of something that is actually spiritual in essence or is beyond the range or power of the eyes or mind to grasp as a whole.

【Dream】 is the general term for the ideas or images present to the mind in sleep.

In extended use  【dream】 , like  【daydream】 , suggests vague or idle, commonly happy, imaginings of future events or of nonexistent things.

【Nightmare】 applies to a frightful and oppressive 【dream】 which occurs in sleep or, by extension, to a 【vision】 or, sometimes, an actual experience which inspires terror or which cannot easily be shaken off.