I. ˈdiŋ-kəm adjective
Etymology: English dialect dinkum, noun, work, share of work
Date: 1905
Australian & New Zealand : authentic , genuine — often used with fair
I was fair dinkum about my interest in their culture — Percy Trezise
II. adverb
Date: 1915
Australian & New Zealand : truly , honestly — often used with fair ; often used interjectionally