'backcast' originates from English, specifically the compound of 'back' + 'cast', where 'back' meant 'backward' and 'cast' meant 'to throw' or 'to project'.

'cast' comes via Old Norse 'kasta' and Old English usages of 'cast' (meaning to throw or to shape), while 'back' comes from Old English 'bæc'; the compound 'backcast' is a modern formation patterned on 'forecast' and emerged in technical contexts (e.g., forecasting, climatology) in the 20th century.

Initially components suggested 'throw/turn back' in a literal sense, but the compound came to mean 'to project or estimate backward'—specifically to produce estimates for past values using forecasting methods.