masquerade costume vs fancy dress

masquerade costume and fancy dress both are nouns.

Word	Noun	Adjective	Verb	Adverb
masquerade costume	Yes	No	No	No
fancy dress	Yes	No	No	No

As nouns, masquerade costume and fancy dress are synonyms defined as:

masquerade costume and fancy dress: a costume worn as a disguise at a masquerade party

Other synonyms of masquerade costume include masquerade.

masquerade costume (noun)	fancy dress (noun)
a costume worn as a disguise at a masquerade party	a costume worn as a disguise at a masquerade party