By God's grace. Introduced into English charters in 1106; as much as to say, “dei non hominum gratia,” by divine right and not man's appointment. The archbishops of Canterbury from 676 to 1170 assumed the same style.
From the time of Offa, King of Mercia (A.D. 780), we find occasionally the same or some similar assumption as, Dei dono, Christo donante, etc. The Archbishop of Canterbury is now divina providentia.
Dei Gratia omitted on a florin. (See Graceless Florin.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894