'apoplectical' originates from Greek, specifically the word 'apoplēxia', where 'apo-' meant 'away' and 'plēx/plekt-' (from 'plēssō' / 'plēxis') meant 'a striking' or 'a blow'.

'apoplectical' passed into Late Latin as 'apoplexia'/'apoplecticus', then into Medieval and Early Modern English as 'apoplectic' and the variant adjective form 'apoplectical'.

Initially, it meant 'struck down by a seizure' (i.e., relating to apoplexy), but over time it also acquired the figurative meaning of 'extremely angry' (furious).