1. happening by chance or accident; not planned or expected
Usage: formal
2. coming from outside; not inherent or natural to something
Usage: formal
3. developing in an unusual or abnormal position
Usage: biology

Examples

• The discovery was purely adventitious, not the result of careful research.
• Adventitious sounds from the street interrupted the quiet meeting.
• The plant developed adventitious roots along its stem after the flood.
• His success seemed adventitious rather than earned through hard work.
• The adventitious meeting led to an unexpected business partnership.
• Adventitious buds appeared on the tree trunk after it was damaged.
• The error was adventitious and not part of the original design.