a. [ Cf. F. occasionnel. ] 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. [ 1913 Webster ]

The . . . occasional writing of the present times. Bagehot. [ 1913 Webster ]

2. Produced by accident; as, the occasional origin of a thing. [ Obs. ] Sir T. Browne. [ 1913 Webster ]

3. Of or pertaining to an occasion or to occasions; intended for a specific occasion; for use only when needed, and not regularly. [ PJC ]

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. [ 1913 Webster ]

n. (Metaph.) The system of occasional causes; -- a name given to certain theories of the Cartesian school of philosophers, as to the intervention of the First Cause, by which they account for the apparent reciprocal action of the soul and the body. [ 1913 Webster ]

n. Quality or state of being occasional; occasional occurrence. [ R. ] [ 1913 Webster ]

adv. In an occasional manner; on occasion; at times, as convenience requires or opportunity offers; not regularly. Stewart. [ 1913 Webster ]

The one, Wolsey, directly his subject by birth; the other, his subject occasionally by his preferment. Fuller. [ 1913 Webster ]