'antimony(III)' is formed from the English noun 'antimony' combined with the Roman numeral '(III)' indicating the +3 oxidation state. The English 'antimony' ultimately derives from Medieval Latin 'antimonium' and Old French 'antimoine'; the chemical symbol 'Sb' comes from the Latin 'stibium'.

'antimony' developed from Medieval Latin 'antimonium' and Old French 'antimoine' into modern English 'antimony'; modern chemical nomenclature later appended oxidation-state notation (e.g. '(III)') to denote specific valence states, giving 'antimony(III)'.

Originally 'antimony' referred broadly to the element/substance (and historically to its medicinal or cosmetic uses); over time, chemical nomenclature introduced specific oxidation-state notation so that 'antimony(III)' now specifically denotes antimony in the +3 oxidation state and its compounds.