To apprehend means to arrest or capture someone, usually a criminal or suspect. When police apprehend a thief, they catch and take the person into custody. You might read in a news story that authorities apprehended a suspect after a careful investigation, or that a fugitive was finally apprehended at the border.

The word carries a sense of official action and authority. It's more formal than simply “catching” someone. Police officers, FBI agents, or security guards apprehend people; they don't just grab them. The word suggests a lawful seizure by someone with the power to make arrests.

Apprehend also means to understand or grasp something with your mind, especially something difficult or abstract. A student might struggle to apprehend a complex theory in science class, or finally apprehend how fractions work after weeks of practice. When you apprehend an idea, you truly get it: you understand it deeply and can work with it.

Related to this second meaning is apprehension, which can also mean understanding or a fearful feeling about something that might happen. If you feel apprehension before a big presentation, you're worried or anxious about it. Someone might approach a challenge with apprehension, unsure of what lies ahead.