Done, said or believed without a good enough reason. You use it when someone acted and the reason they had does not hold up: an unjustified fear, unjustified criticism, an unjustified pay rise, unjustified confidence. It says the reason was missing or too weak this time — it does not go as far as saying no reason could ever exist. That is a real and useful difference from 'unjustifiable'. It works before a noun and after 'be', and it pairs naturally with words for feelings and reactions ('her worry turned out to be unjustified'), which is where it is gentlest — sometimes it means little more than 'it turned out there was nothing to worry about', with no blame at all. There is also a completely separate technical use in word processing and printing, where 'unjustified' text is text with a ragged edge, not lined up straight down both sides — nothing to do with fairness.