accidental

associated by chance and not an integral part

• “poetry is something to which words are the accidental, not by any means the essential form” Frederick W. Robertson
• “they had to decide whether his misconduct was adventitious or the result of a flaw in his character”

occurring or appearing or singled out by chance

• “their accidental meeting led to a renewal of their friendship”
• “seek help from casual passers-by”
• “a casual meeting”
• “a chance occurrence”

without intention (especially resulting from heedless action)

• “with an inadvertent gesture she swept the vase off the table”
• “accidental poisoning”
• “an accidental shooting”

a musical notation that makes a note sharp or flat or natural although that is not part of the key signature