Sicilies
Usage notes
Solely used with respect to the historical Two Sicilies, the kingdoms formed from the Kingdom of Sicily after a successful revolt in 1282 (the Sicilian Vespers) brought about partition, with the then-ruling Angevins managing to keep the peninsular lands. Each part titled itself Kingdom of Sicily (although modern scholars refer to the peninsular lands as Kingdom of Naples). The Sicilies were finally recombined in 1816 as the Kingdom of the Two Sicilies, which was later absorbed into the Kingdom of Italy during Italian unification.
Sicilies is an exception to the rule that proper nouns ending in y add an s to form their plural (as in Germanys and Marys).