Briticism vs Britishism

Briticism and Britishism both are nouns.

Word	Noun	Adjective	Verb	Adverb
Briticism	Yes	No	No	No
Britishism	Yes	No	No	No

As nouns, Briticism and Britishism are synonyms defined as:

Briticism and Britishism: an expression that is used in Great Britain (especially as contrasted with American English)

Other synonyms of Briticism include Anglicism.

Briticism (noun)	Britishism (noun)
an expression that is used in Great Britain (especially as contrasted with American English)	a custom that is peculiar to England or its citizens
	an expression that is used in Great Britain (especially as contrasted with American English)