By serendipity; by unexpected good fortune.(adjective)
Good, beneficial, favorable, etc..(adjective)
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Use "serendipitous" in a sentence
"I use the term serendipitous as it applies to my good fortune."
"There is nothing like the loquacious mayhem of a summer picnic with close friends to bring out the very best in serendipitous, anarchic explorations of wine, food and opinions."
"Catching the killer or finding out his identity has been frequently termed serendipitous: some streak of luck suddenly entered the investigations."