'unpredictable' definitions:

Definition of 'unpredictable'

From: WordNet
adjective
Not capable of being foretold [ant: predictable]
adjective
Unknown in advance; "an unpredictable (or indeterminable) future"
adjective
Not occurring at expected times [syn: irregular, unpredictable]

Synonyms of 'unpredictable'

From: Moby Thesaurus