'architrave' originates from Late Latin 'architrāvus', ultimately via Greek 'arkhitrabēs', where 'arkhi-' meant 'chief' and the element related to Latin 'trabs' meant 'beam'.

'architrabēs' (Greek) passed into Late Latin as 'architrāvus' and through Medieval/Neo-Latin and French/Italian usage became the English word 'architrave' in early modern usage.

Initially it meant 'chief beam' (the main beam across the top of a structure); over time the sense broadened to include the moulded frame or decorative beam above doors and windows, which is the common modern meaning.