To dissatisfy means to fail to meet someone's expectations or needs, leaving them disappointed or unhappy with something. When a restaurant meal dissatisfies a customer, the food might be cold, bland, or not what they ordered. When a book's ending dissatisfies readers, they feel let down because the story didn't resolve the way they hoped.

The word describes that specific feeling of “this isn't good enough” or “this isn't what I wanted.” A teacher might be dissatisfied with a student's rushed homework, not because it's terrible, but because she knows the student can do better work. A coach might feel dissatisfied after a game his team won, because the players didn't follow the game plan or play up to their potential.

Notice that being dissatisfied is different from being angry or upset. It's more about unmet expectations than strong negative emotions. You might feel dissatisfied with how you played in a soccer game even though your team won. That dissatisfaction can actually be useful because it shows you care about improvement. The related noun is dissatisfaction, and the adjective is dissatisfied.