occasion

n. 1 a special event or happening. B time of this. 2 reason, need. 3 suitable juncture, opportunity. 4 immediate but subordinate cause. v. Cause, esp. Incidentally.  on occasion now and then; when the need arises. [latin occido occas- go down]

n. A falling out, happening, or coming to pass; hence, that which falls out or happens; occurrence; incident.