From Old French 'a dieu' (to God), a shortened form of 'I commend you to God' — a medieval parting formula reflecting real uncertainty about whether one would meet again.
A farewell; an expression used to bid someone goodbye, often with a sense of finality
Borrowed directly from Old French 'a dieu,' a contraction of 'je vous commande à Dieu' (I commend you to God). The phrase combines the preposition 'à' (to) and 'Dieu' (God), from Latin 'Deus.' The expression was a standard parting formula in medieval Europe, reflecting the genuine
Nearly every major European farewell formula originally invoked God: English 'goodbye' (God be with ye), Spanish 'adiós' (a Dios), Welsh 'duw' (God), and Irish 'slán' (health/salvation). The secularization of parting words is a surprisingly recent phenomenon — most took centuries to lose their theological freight.