'antimonial' originates from New Latin/Latin, specifically the word 'antimonium', where 'antimonium' meant 'antimony' (the element or its compounds) and the suffix '-al' formed an adjective meaning 'relating to'.

'antimonium' (Late Latin) gave rise to Old French 'antimoine' and English 'antimony'; the adjective 'antimonial' developed in English by adding the suffix '-al' to the stem of 'antimony', yielding the sense 'relating to antimony' and the noun sense for antimony-containing preparations.

Initially it referred directly to the element or its compounds ('antimony'); over time it developed the adjectival sense 'relating to or containing antimony' and a noun sense for medicinal or chemical preparations containing antimony.