'arvo' originates from Australian English, specifically as a clipped (informal) form of the word 'afternoon', where 'after' meant 'later' and 'noon' meant 'midday'.

'arvo' changed from an informal shortening of the Modern English word 'afternoon' and eventually became established in Australian colloquial speech as 'arvo'.

Initially, it meant a simple shortened form of 'afternoon', and over time it evolved into a widely used informal Australian term meaning 'the afternoon'.