'as-cast' is a compound of the particle 'as' (used to indicate manner or condition) and the past participle 'cast' (from the verb 'cast').

The element 'as' goes back to Old English forms such as 'alswa'/'eallswa' meaning 'in the manner of', while 'cast' comes from the verb 'cast' (Old Norse 'kasta' / Proto-Germanic *kastjanan) meaning 'to throw' or 'to shape by throwing/casting'; the compound developed in technical contexts to describe items 'in the condition they were cast'.

Originally referring simply to something 'thrown' or 'shaped by casting', the combined term came to mean specifically 'in the condition produced by the casting process, without subsequent treatment'.