A common Australian term meaning real or honest that can be used in a couple of contexts. eg He is a fair dinkum idiot or when something is amazing or surprising you just say ‘fair dinkum!’
That’s as near as I can get to common use. It’s like we say ‘fair suck of the Sav’ when we feel someone has had more than enough of a ‘fair share’ a ‘Sav’ is a horrible red-coloured sauage.
Much of our slang has its origin in England.
But ‘fair dinkum’ above all else, is used to indicate ‘the real thing’ - it’s the truth.
This thread has been amazing :-)