unpredictable
🇺🇸
/ˌʌnprɪˈdɪktəbl/
🇬🇧
/ˌʌnprɪˈdɪktəbl/
Not able to be known in advance because it changes often or depends on many things.
The weather is unpredictable, so always carry an umbrella just in case.
A person whose actions or behavior cannot be guessed beforehand.
He is so unpredictable that you never know how he will react.