any custom, manner, characteristic, or quality peculiar to or associated with the British people
3.
the aggregate of such qualities regarded as characteristic of a British person
His cool reserve is just part of his Britishism
Word origin
[1880–85; british + -ism]This word is first recorded in the period 1880–85. Other words that entered Englishat around the same time include: Chief of Staff, impressionism, jackpot, quotation mark, rain check-ism is a suffix appearing in loanwords from Greek, where it was used to form action nounsfrom verbs (baptism). On this model, -ism is used as a productive suffix in the formation of nouns denoting action or practice,state or condition, principles, doctrines, a usage or characteristic, devotion oradherence, etc. (criticism; barbarism; Darwinism; despotism; plagiarism; realism; witticism; intellectualism)