Adding the prefix dis- to a word often changes the word into its antonym (opposite).
like / dislike
honest / dishonest
obey / disobey
However, sometimes adding the prefix dis- has a different effect on a word. For example, the word disinterested does not mean the opposite of interested.
Matthew didn't like either team so he was a disinterested observer at the match.
The above sentence doesn't mean that Matthew wasn't interested in the match. It actually means that he was neutral or impartial.
In this worksheet you can think about how the prefix dis- affects the meaning of words in different ways. You may find a dictionary helpful.