The adverb has 3 meanings:
Meaning #1:
without advance planning
Synonyms: by chance, circumstantially, unexpectedly
Antonym: deliberately (meaning #1)
Derived from adjective: accidental (meaning #2)
Meaning #2:
in an incidental manner
Synonyms: incidentally, by chance
Meaning #3:
without intention; in an unintentional manner
Synonym: unintentionally
Antonym: deliberately (meaning #1)
Derived from adjective: accidental (meaning #3)




