Early 17th century. From accustomed + -ly. Compare Old French acostumeement, acustumeement, acustumeiement, Middle French acoustumeement, accoustumeement, Old Occitan acostumadamen.
Definition of accustomedly in US English:
accustomedly
adverbəˈkʌstəmdli
In the accustomed manner; usually, customarily.
Origin
Early 17th century. From accustomed + -ly. Compare Old French acostumeement, acustumeement, acustumeiement, Middle French acoustumeement, accoustumeement, Old Occitan acostumadamen.