For the meaning of "to arrest":
* Seize: This emphasizes taking someone into custody.
* Capture: This emphasizes catching someone who is trying to escape.
* Take into custody: This is a more formal way of saying "arrest".
* Detention: This is a more general term for keeping someone in custody.
For the meaning of "to understand":
* Grasp: This emphasizes a firm understanding of something.
* Comprehend: This is a more formal synonym for "understand".
* Perceive: This emphasizes the process of coming to understand something.
* Realize: This emphasizes the moment of understanding.
For the meaning of "to fear":
* Dread: This emphasizes a strong fear of something.
* Fear: This is a more general term for apprehension.
* Be afraid of: This is a more informal way of saying "apprehend".
* Be anxious about: This emphasizes a feeling of worry and uncertainty.
To choose the best synonym, consider the specific situation and the intended meaning.