In a manner that joins, attaches, or adds something to something else; in a supplementary or supporting way.
From adjunctive plus the -ly suffix (which creates adverbs). This adverb form allows speakers to describe how something functions in a joined or supporting capacity.
When something happens 'adjunctively,' it's working alongside something else in a supporting role—it's the adverb way of describing that supplementary, connecting function.
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