I. |aksə|dent ə l adjective
Etymology: Middle English, from Middle French, from accident + -al
1. : arising from or produced by extrinsic, secondary, or additional causes or forces : not innate, intrinsic, or of the real nature of : nonessential
some of the colors were mineral, in the rock itself: but others were accidental due to water from the melting snow — T.E.Lawrence
whether this paralogistic procedure is essential or accidental to his doctrine — T.H.Green
2. : occurring sometimes with unfortunate results by chance alone:
a. : unpredictable : proceeding from an unrecognized principle, from an uncommon operation of a known principle, or from a deviation from normal
b. : happening or ensuing without design, intent, or obvious motivation or through inattention or carelessness
accidental collision
accidental shooting
accidental loss
3. : having reference to a logical accident : not essential : contingent , extrinsic
being dark-haired is an accidental property of a man — Arthur Pap
4. : relating to an accidental in music or to its prefixed sign
5. of a bird : found outside the normal geographic range or season
a common migrant, accidental in winter
Synonyms:
fortuitous , adventitious , contingent , casual , incidental : when it is used in reference to events, accidental may stress lack of intent or indicate an unusual operation of natural causes
so plain that Thady's presence … was accidental, and that the attack could not have been premeditated — Anthony Trollope
In reference to qualities, accidental indicates absence of an essential or innate characteristic
their search for the typical and their avoidance of anything that might be considered accidental — John Dewey
fortuitous stresses chance and minimizes the idea of definite analyzable cause
I do not look upon public events either as fortuitous or absolutely derivable either from the wisdom or folly of man — William Cowper
adventitious stresses the extrinsic, additional, irrelevant, or nonessential
regular repetition of forms, uniformly spaced, the architect depending only upon adventitious ornamentation for variety — John Dewey
in works of imagination and sentiment … meter is but adventitious to composition — William Wordsworth
contingent stresses unpredictability and uncertainty, especially in future events
countless contingent difficulties … many of which must necessarily arise, though the exact nature of them could not be anticipated — J.A.Froude
It also indicates dependence on something else for existence or occurrence
the resistance that we may meet with is contingent on the enemy's continued strength
incidental stresses a secondary or minor nature, regardless of manner of origin
war … the comprehensive business of the German … to the British … was an incidental adventure — H.G.Wells
casual stresses dependence on chance and lack of prearrangement or predictability
it was no casual reencounter. He had been enticed into the place — J.A.Froude
the causal allusion, the chance reference — Henry Adams
casual and incidental may indicate occurrences actually planned and intended but presented as if by chance
the pupil must be aroused … his curiosity must be awakened by an incidental explanation, a casual remark — C.H.Grandgent
II. noun
( -s )
Etymology: Middle English, from accidental, adjective
1. logic : a nonessential property
2. : nonessential
3.
a. : a chromatically altered note (as a sharp or flat) in a musical composition that is usually foreign to the key indicated by the signature
b. : the prefixed sign (as ♯ or ♭) indicating a chromatically altered note
4. : warp ends not usually included in the treadling pattern in hand weaving
5. : a fingerprint showing two or more pattern types or other peculiarities making classification difficult