General opposites:
* Misunderstand: This implies a complete or partial failure to grasp the meaning of something.
* Not understand: This is a simple negation of understanding.
* Be confused: This implies a lack of clarity or a sense of disorientation.
* Be ignorant: This refers to a lack of knowledge or awareness.
More specific opposites:
* Disagree: This implies a difference of opinion or interpretation.
* Ignore: This means to deliberately pay no attention to something.
* Reject: This indicates a refusal to accept or believe something.
* Misinterpret: This means to understand something incorrectly.
The best opposite for "understand" will depend on the specific situation.