Occasional

Part of speech: adjective (a.)

1. Of or pertaining to an occasion or to occasions; 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.] Sir T. Browne. 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.