'antrustion' originates from Medieval Latin 'antrustio' and Old French 'antrustion', ultimately derived from a West Germanic (Frankish) source; the elements relate to the idea of being bound by trust or an oath.

'antrustion' passed from a West Germanic/Frankish formation into Medieval Latin as 'antrustio' and Old French 'antrustion', and was used in Frankish legal and court contexts before appearing in Middle English texts as an archaic term.

Initially, it referred more generally to those 'entrusted' or bound by oath to a lord; over time it came to denote specifically a member of the royal or lordly household guard and is now archaic.