'consubstantialist' originates from Modern English, formed from the adjective 'consubstantial' + the agent suffix '-ist', where Latin 'con-' meant 'together' and Latin 'substantia' meant 'substance'.

'consubstantial' came into theological use from Medieval Latin 'consubstantialis'; English then formed 'consubstantial' and later the agent noun/adjective 'consubstantialist' to denote someone holding or relating to that doctrine.

Initially the root idea meant 'of the same substance' (pertaining to shared substance); over time the derived English form came to refer specifically to the doctrine of consubstantiation and to persons who hold or describe that position.