in a manner relating to or characteristic of an edict; by official proclamation or decree.
From 'edictal' (adjective) with the adverbial suffix '-ly', creating an adverb that describes actions done in the manner of a legal edict.
This is an extremely rare adverb—lawyers might say something was done 'edictally' (by decree), but most English speakers would just say 'by edict' or 'officially' instead.
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