'heteroousian' originates from Greek, specifically the element 'hetero-' meaning 'different' and the noun 'ousia' meaning 'essence' or 'substance', formed as the adjective 'heteroousios' ('of different substance').

'heteroousian' developed from the Greek theological term 'heteroousios' used in early Christological debates; it passed into Late Latin/Medieval theological Latin as forms like 'heteroousius' and later entered English usage in histories and theological writings as 'heteroousian'.

Initially, it meant 'of different substance' in the specific context of Trinitarian/Christological theology; over time the term has remained narrowly theological with essentially the same core meaning.