noun

• 1rare A chance occurrence or circumstance; (contextually) a fortuitous event, a mishap. In non-count use: fortuitous disposition, chance. Compare "accident".

• 2US Usually with capital initial. Preceded by a possessive, as a mock title of respect given to a person who has succeeded to an office (especially the presidency of the United States) by chance or mishap, such as the death of the previous incumbent. Chiefly in "His Accidency".