Mentally means in your mind rather than physically or out loud. When you do something mentally, you're using your thoughts, imagination, or memory instead of your body or voice.

If your teacher asks you to solve 47 plus 35 mentally, she wants you to figure it out in your head without writing anything down or using a calculator. When you mentally prepare for a big game or performance, you imagine yourself succeeding and think through what you'll do. Athletes often rehearse their routines mentally before competing, picturing each move in their minds.

The word also describes your psychological or emotional state. Someone who is mentally exhausted feels drained from thinking hard or dealing with stress, even if they haven't been physically active. A person who is mentally strong can handle difficult situations without falling apart.

You might mentally note something worth remembering, or mentally calculate whether you have enough allowance money for something you want. When you're reading a novel, you mentally picture the characters and settings the author describes. This mental work happens entirely in your mind, invisible to everyone else, yet it's often just as real and important as anything you do with your hands or voice.