Late Middle English; earliest use found in Guy de Chauliac's Grande Chirurgie. From classical Latin allēgāt-, past participial stem of adlēgāre, allēgāre to send as an intermediary or representative, to commission, to adduce, urge, plead, in post-classical Latin also to allege, assert as fact, to plead, argue, to confirm from al-, variant of ad- + legāre.