Adjective
not scheduled or not on a regular schedule
Source: WordNetHe had long nostril hairs, powerfully intimidating, like an unscheduled nightmare. Charles Bukowski
Today is declared an unscheduled holiday. Lois Lowry
Real travel requires a maximum of unscheduled wandering, for there is no other way of discovering surprises and marvels, which, as I see it, is the only good reason for not staying at home. Alan Watts
I believe in the joyous power of an unscheduled dance break. Sophia Bush
The first thing any comedian does on getting an unscheduled laugh is to verify the state of his buttons. W. C. Fields
an unscheduled meeting Source: Internet