In a manner that is open to exception or objection; questionably or dubiously.
From 'exceptionable' + '-ly' adverbial suffix. Adds the adverbial layer to the adjectival form to describe how something is done.
Adding '-ly' to already-complex words shows how English speakers keep building on roots—'exceptionably' is technically correct but sounds so unwieldy that it barely survives in modern writing.
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