show window vs showcase

show window and showcase both are nouns.

Word	Noun	Adjective	Verb	Adverb
show window	Yes	No	No	No
showcase	Yes	No	No	No

As nouns, show window and showcase are synonyms defined as:

show window and showcase: a setting in which something can be displayed to best effect

show window (noun)	showcase (noun)
a window of a store facing onto the street; used to display merchandise for sale in the store	a glass container used to store and display items in a shop or museum or home
a setting in which something can be displayed to best effect	a setting in which something can be displayed to best effect