IPA: /ʌnˈdʒʌstɪfaɪd/
KK: /ʌnˈdʒʌstəˌfaɪd/
Not having a good reason or explanation; lacking justification.
The decision to fire him was unjustified and caused a lot of confusion.
Unjustified → It is formed from "un-" (meaning not) and "justified" (from Latin "justificare", meaning to make just or right). The word "unjustified" means not made just or lacking justification.
Think of 'not' ('un-') making something 'just' or 'right' ('justified') — that's why unjustified means lacking justification.