fantasize vs fantasy

fantasize is not a noun while fantasy is a noun.

Word	Noun	Adjective	Verb	Adverb
fantasize	No	No	Yes	No
fantasy	Yes	No	Yes	No

As verbs, fantasize and fantasy are synonyms defined as:

Other synonyms of fantasize include fantasise.

fantasize (noun)	fantasy (noun)
	imagination unrestricted by reality
	something many people believe that is false
	fiction with a large amount of imagination in it

fantasize (verb)	fantasy (verb)
indulge in fantasies	indulge in fantasies
portray in the mind