is perhaps the most common colloquial
linguistic export from Australia
Originally a bush or folk saying/exclaimation, it entered popular currency around the 1900s.
It is popularly used in two conversational forms: a question, and a statement of fact. As a question, it means "is that right?" or perhaps "are you quite sure?". As a statement of fact, it means "absolutely correct".
The origin of the phrase is said to have mutated from early convict "fair drinking".
"Fair dinkum, that was a bloody good game of footy."
"Yair, fair dinkum."
"So be fair dinkum, and vote yes, yes for an Australian Head of State." -- Rt Hon Bob Hawke, Former Prime Minister of Australia, 31 October 1999