mannerism vs idiosyncrasy

mannerism and idiosyncrasy both are nouns.

Word	Noun	Adjective	Verb	Adverb
mannerism	Yes	No	No	No
idiosyncrasy	Yes	No	No	No

As nouns, mannerism and idiosyncrasy are synonyms defined as:

mannerism and idiosyncrasy: a behavioral attribute that is distinctive and peculiar to an individual

Other synonyms of mannerism include foible.

mannerism (noun)	idiosyncrasy (noun)
a deliberate pretense or exaggerated display	a behavioral attribute that is distinctive and peculiar to an individual
a behavioral attribute that is distinctive and peculiar to an individual