'antithyroidal' originates from Modern English and New Latin, specifically the combining element 'anti-' from Greek 'anti' where it meant 'against', the element 'thyroid' from Modern Latin 'thyreoideus' (ultimately from Greek 'thyreoeidēs'), and the adjectival suffix '-al' from Latin '-alis' used to form adjectives.

'thyroid' entered English via Modern Latin 'thyreoideus' (from Greek 'thyreoeidēs' meaning 'shield-like') and medical usage created the compound 'antithyroid' (late 19th–early 20th century); 'antithyroidal' developed by adding the English/Latin-derived suffix '-al' to form an adjective describing agents that act against the thyroid.

Initially the components literally signified 'against the thyroid (gland)', and over time the compound came to be used specifically for drugs or agents that inhibit thyroid function or thyroid-hormone action.