'adat' originates from Arabic, specifically the word 'ʿāda', where 'ʿāda' meant 'custom' or 'habit'.

'ʿāda' was adopted into Malay and Indonesian languages as 'adat', retaining its meaning of 'custom' or 'tradition'.

Initially, it meant 'custom' or 'habit', and this meaning has largely remained the same in modern usage.