Donk is absent from many dictionaries, but
Wiktionary has four separate entries, with about 15 definitions!
Merriam-Webster says it means donkey. The Shorter Oxford says donkey or donkey engine, which possibly provides the link to the Australian usage for an engine in a car, boat, etc. It can also be used for a sound, as in this passage from a 2018 article in
The Age about lawn bowls:
I head out onto the greens to watch. It's warm and still. There's the cawing of magpies, the soft donk of bowl on bowl, the sedative murmur of geriatrics chatting.
I'll add
donk as a rare word.
