'arianist' originates from Latin/Greek, specifically from the name 'Arius' (Latin 'Arius', from Greek 'Ἄριος' or similar forms), where the name identifies the 4th-century presbyter Arius whose followers formed Arianism.

'arianist' developed from the adjective and noun 'Arian' (meaning 'of or relating to Arius' or 'Arianism') plus the agentive suffix '-ist'; the name of the 4th-century figure 'Arius' gave rise to 'Arian', which through English word-formation became 'arianist'.

Initially it specifically meant 'a follower of Arius (the historical person)', but over time it has been used more broadly for anyone who holds Arian-like subordinationist Christology or, occasionally, used figuratively to describe similar heterodox positions.