Accidental describes what was not planned or intended. It means happening by accident or happening as an accident, as in an accidental discovery and an accidental injury. Happening by chance or unexpectedly; taking place not according to the usual course of things; casual; fortuitous; as, an accidental visit. Accidental primarily refers to what occurs by chance: an accidental meeting. It can also mean subordinate or nonessential: Poetry is something to which words are the accidental, not by any means the essential form (Frederick W. Robertson). Definition of accidental adjective in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. An accidental event happens by chance or as the result of an accident, and is not deliberately intended. The jury returned a verdict of accidental death. His hand brushed against hers; it could have been either accidental or deliberate. Accidental, casual, fortuitous all describe something outside the usual course of events. Accidental implies occurring unexpectedly or by chance: an accidental blow. ACCIDENTAL definition: happening by chance or accident; not planned; unexpected. See examples of accidental used in a sentence. Anything accidental happens by chance or unintentionally. People don't mean to do accidental things. The comprehensive definition of accidental. Includes pronunciation, synonyms, etymology, and usage examples to help you master this word. ACCIDENTAL meaning: 1. happening or existing by chance: 2. a sign showing that there is a temporary change from the…. Learn more.