The act of forming or styling hair into a bun, or in Australian/British slang, a barbecue or outdoor cooking event.
From 'bun' with the gerund -ing suffix; in Australian English, 'bunning' comes from 'bun' in the sense of a sausage served in a bread roll, making it short for 'sausage bun cooking.'
Australians transformed a hairstyle word into their word for grilling meat—this shows how the same word can have completely different meanings in different English-speaking countries!
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