barbican vs barbacan

barbican and barbacan both are nouns.

Word	Noun	Adjective	Verb	Adverb
barbican	Yes	No	No	No
barbacan	Yes	No	No	No

As nouns, barbican and barbacan are synonyms defined as:

barbican and barbacan: a tower that is part of a defensive structure (such as a castle)

barbican (noun)	barbacan (noun)
a tower that is part of a defensive structure (such as a castle)	a tower that is part of a defensive structure (such as a castle)