1.adjectiveAccidental; as the result of some unforeseen happening or series of events; unexpected; resulting from an event without the foresight, expectation, aid, or design of the person by whose agency it was caused; unintentional.
"That the injury was by accident is not questioned."
2.adverbAccidentally; unintentionally; without meaning to; as the result of an event not expected, aided, or willingly planned.
"Sorry. I knocked over the vase by accident."
3.adverbAs the result of some undesigned, unintended, unrelated, natural, or random occurrence; as the unexpected and unforeseen result of formerly unrelated factors.
"The car got totaled by accident; a giant snowdrift fell off the church roof."
4.adverbBy chance; unexpectedly; as the result of an unrelated series of events.
"I hadn't seen her for years, but I ran into her by accident at the store."