unpredictable

adj

1. Unable to be predicted.

   “It has, therefore, always been a major problem for South African railways to cater adequately for this unpredictable city; three stations have had to be built on the present site during the last fifty years.”

   “Sharks are not unpredictable; for the most part, they do exactly what an apex predator is expected to do.”

noun

1. An unpredictable thing.

   “Other unpredictables, like the recent unexpected blizzards and those of 2 years ago, or a hurricane can cost us many thousands of dollars, and have a severe impact on equipment and facilities.”