'ashfall' originates from English, specifically the compound of 'ash' and 'fall', where 'ash' meant 'residue of burned material' and 'fall' meant 'a falling or descent'.

'ashfall' was formed in Modern English by compounding 'ash' + 'fall' and has been used in geological and volcanic contexts (especially since the 19th century) to describe deposits of ash from eruptions.

Initially it meant 'the falling of ash'; over time this core sense has remained stable and now specifically refers to ash deposited from volcanic activity.