incidentally - adverb
Grammar.com's section on the Parts of Speech discusses the demise of -ly adverbs. Click here for that discussion.
Example: They met incidentally at the convention a year before their marriage.
"incidentally - correct spelling." Grammar.com. STANDS4 LLC, 2018. Web. 24 Feb. 2018. <https://www.grammar.com/incidentally-correct-spelling>.
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