In a way that deepens or becomes increasingly deep or profound; with increasing depth or complexity.
From 'deepening' (the present participle of 'deepen') plus the adverb suffix '-ly.' The formation shows how English builds adverbs from present participles to describe manner of action.
Deepeningly is a lovely but rare adverb—it's the kind of word that poets or philosophers might use to describe how understanding grows more complex, showing how English creates adverbs for concepts we don't use constantly but desperately need sometimes.
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