The prefix "en-" generally means "to cause to be" or "to make." In the words "enable" and "endanger," it indicates a transformation or action.
- In "enable," it means to make able or to facilitate something.
- In "endanger," it means to cause to be in danger or to put at risk.
So, in both cases, "en-" is used to indicate that something is being caused or changed in a certain way.