signior vs signor

signior and signor both are nouns.

Word	Noun	Adjective	Verb	Adverb
signior	Yes	No	No	No
signor	Yes	No	No	No

As nouns, signior and signor are synonyms defined as:

signior and signor: used as an Italian courtesy title; can be prefixed to the name or used separately

signior (noun)	signor (noun)
used as an Italian courtesy title; can be prefixed to the name or used separately	used as an Italian courtesy title; can be prefixed to the name or used separately