If you dismiss something, you decide or say that it is not important enough for you to think about or consider.

If you dismiss something from your mind, you stop thinking about it.

When an employer dismisses an employee, the employer tells the employee that they are no longer needed to do the job that they have been doing.

If you are dismissed by someone in authority, they tell you that you can go away from them.

When a judge dismisses a case against someone, he or she formally states that there is no need for a trial, usually because there is not enough evidence for the case to continue.