showpiece vs collector's item

showpiece and collector's item both are nouns.

Word	Noun	Adjective	Verb	Adverb
showpiece	Yes	No	No	No
collector's item	Yes	No	No	No

As nouns, showpiece and collector's item are synonyms defined as:

showpiece and collector's item: the outstanding item (the prize piece or main exhibit) in a collection

Other synonyms of showpiece include piece de resistance.

showpiece (noun)	collector's item (noun)
the outstanding item (the prize piece or main exhibit) in a collection	the outstanding item (the prize piece or main exhibit) in a collection