In a manner relating to diction; with regard to the choice and use of words.
From 'dictional' + '-ly' (adverbial suffix). The formation follows standard English patterns for creating adverbs from adjectives.
A writer might improve 'dictionally' by learning to choose more vivid and precise verbs—it's the adverb form showing how someone's word choices are developing.
Complete word intelligence in one call. Free tier — 50 lookups/day.