Some common synonyms of accidental are casual, contingent, and fortuitous. While all these words mean not amenable to planning or prediction, accidental stresses chance. 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 adjective version of this word is accidental, and they are both derived from the word accident, which means an unfortunate event that was unintended. The word accident can be traced to Medieval English, when it was probably borrowed from Medieval French. Find 53 different ways to say ACCIDENTAL, along with antonyms, related words, and example sentences at Thesaurus.com. 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 definition: 1. happening or existing by chance: 2. a sign showing that there is a temporary change from the…. Learn more. ACCIDENTAL meaning: 1. happening or existing by chance: 2. a sign showing that there is a temporary change from the…. Learn more. 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. These adjectives apply to what happens unintentionally. 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).