/ˌæk.sɪˈden.t̬əl/
[adjective] Happening by chance or without being planned. An accidental event is something that nobody intended or expected to happen.
The word 'accidental' literally descends from the Latin word for 'falling' — as if bad luck were simply gravity catching you off guard.
The story of 'accidental' begins in ancient Rome with a remarkably physical verb: the Latin 'cadere', meaning 'to fall'. From this root, Roman writers built the compound 'accidere' — formed from 'ad' (towards or upon) and 'cadere' — which meant something like 'to fall upon' or 'to happen'. It carried the same unpredictable quality that a stumble has: something that arrives without invitation, dropping onto you from nowhere. From 'accidere' came the noun 'accidens', meaning an event that just happens, something not planned or caused by design.
Latin philosophers, particularly those translating Greek thought into Roman terms, gave 'accidens' a more precise and technical meaning. In the philosophy of Aristotle — filtered through Latin scholars — an 'accidens' was a property that a thing might or might not have, as opposed to its essential nature. A rose is essentially a flower, but its redness is an 'accidens': it could, in theory, be white. This philosophical use gave the word a lasting association with the non-essential, the contingent, the things that exist beside the point.
The word moved into medieval French as 'accident', keeping both senses — the everyday meaning of an unexpected event and the philosophical meaning of a non-essential quality. From Old French 'accident', it crossed into Middle English in the 14th century, arriving in texts concerned with both ordinary life and scholarly argument. The adjectival form 'accidental' followed naturally, built from the noun with the common Latin suffix '-alis', meaning 'relating to'. So Latin 'accidentalis' → Old French 'accidentel' → Middle English 'accidental' — each step preserving the core idea of something unplanned and unintended.
What is fascinating is how the word's meaning slowly narrowed over the centuries. In early English use, 'accidental' could still describe something philosophically non-essential or secondary, not merely something caused by bad luck. A 17th-century writer might call the colour of a man's coat 'accidental' simply meaning it was not a defining feature of him as a person. Over time, however, everyday speech gradually crowded out the philosophical sense, and 'accidental' came to mean almost exclusively 'happening by chance' — especially in the context of mishaps, injuries, and unintended consequences.
The family of words that grew from the root 'cadere' — to fall — is surprisingly large and rich in English. Latin 'cadere' gave us 'cadence' (the falling rhythm of music or speech), and 'case' (from Latin 'casus', a falling, a circumstance) via Old French 'cas'. It also produced 'decay' through Latin 'decidere' → Old French 'decair', and 'occasion' from Latin 'occasio', meaning a favourable falling-together of events. Even 'incident' and 'coincidence' share this ancestry, all of them carrying the ghost of something dropping, tumbling, or landing unexpectedly into place. 'Accident' and 'accidental', then, are not just words about bad luck — they are small monuments to the ancient human idea that events fall upon us, rather than rising up from our own intentions.