Accidental

a.	1.	Happening by chance, or unexpectedly; taking place not according to the usual course of things; casual; fortuitous; as, an accidental visit.
	2.	Nonessential; not necessary belonging; incidental; as, are accidental to a play. Accidental chords (Mus.) those which contain one or more tones foreign to their proper harmony. Accidental colors (Opt.) colors depending on the hypersensibility of the retina of the eye for complementary colors. They are purely subjective sensations of color which often result from the contemplation of actually colored bodies. Accidental point (Persp.) the point in which a right line, drawn from the eye, parallel to a given right line, cuts the perspective plane; so called to distinguish it from the principal point, or point of view, where a line drawn from the eye perpendicular to the perspective plane meets this plane. Accidental lights (Paint.) secondary lights; effects of light other than ordinary daylight, such as the rays of the sun darting through a cloud, or between the leaves of trees; the effect of moonlight, candlelight, or burning bodies. - Fairholt.
n.	1.	A property which is not essential; a nonessential; anything happening accidentally. He conceived it just that accidentals . . . should sink with the substance of the accusation. - Fuller.
	2.	(Paint.) Those fortuitous effects produced by luminous rays falling on certain objects so that some parts stand forth in abnormal brightness and other parts are cast into a deep shadow.
	3.	(Mus.) A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.

Noun	1.	accidental - a musical notation that makes a note sharp or flat or natural although that is not part of the key signature
Adj.	1.	accidental - associated by chance and not an integral part; "poetry is something to which words are the accidental, not by any means the essential form"- Frederick W. Robertson; "they had to decide whether his misconduct was adventitious or the result of a flaw in his character" Synonyms: adventitious
	2.	accidental - occurring or appearing or singled out by chance; "their accidental meeting led to a renewal of their friendship"; "seek help from casual passers-by"; "a casual meeting"; "a chance occurrence" Synonyms: chance, casual
	3.	accidental - without intention (especially resulting from heedless action); "with an inadvertent gesture she swept the vase off the table"; "accidental poisoning"; "an accidental shooting" Synonyms: inadvertent

accessory, accident, accidentally, accompanying, addendum, addition, additional, adjunct, ado, adscititious, adventitious, afloat, afoot, aleatory, appendage, appurtenance, appurtenant, ascititious, auxiliary, breve, by-the-way, casually, causeless, chancy, circumstantial, coincident, coincidental, collateral, conditional, contingency, crotchet, current, demisemiquaver, dependent, destinal, dicey, doing, dominant, dominant note, double whole note, eighth note, enharmonic, enharmonic note, eventuating, extra, fatal, fatidic, flat, fluky, fortuitously, going on, half note, happening, happenstance, hemidemisemiquaver, iffy, in hand, in the wind, inadvertent, incidental, indeterminate, inessential, lucky, mere chance, minim, musical note, natural, nonessential, not-self, note, occasional, occurring, odd, on, on foot, ongoing, other, parenthetical, passing, patent note, prevailing, prevalent, provisional, quarter note, quaver, random, report, responding note, resultant, risky, secondary, semibreve, semiquaver, serendipitous, shaped note, sharp, sixteenth note, sixty-fourth note, spiccato, staccato, subsidiary, superadded, superaddition, superfluous, supervenient, supplement, supplemental, supplementary, sustained note, taking place, tercet, thirty-second note, tone, triplet, unanticipated, uncalculated, uncaused, under way, undesigned, undetermined, unessential, unforeseeable, unforeseen, unintentional, unlooked-for, unlucky, unmeant, unpredictable, unpremeditated, unpurposed, unwitting, whole note