Oc·ca·sion·al a.
 1. Occuring at times, but not constant, regular, or systematic; made or happening as opportunity requires or admits; casual; incidental; as, occasional remarks, or efforts.
    The . . . occasional writing of the present times.   --Bagehot.
 2. Produced by accident; as, the occasional origin of a thing. [Obs.]
 Occasional cause Metaph., some circumstance preceding an effect which, without being the real cause, becomes the occasion of the action of the efficient cause; thus, the act of touching gunpowder with fire is the occasional, but not the efficient, cause of an explosion.

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