The prefix "en-" generally means "to cause to be" or "to put into." In the words you mentioned:
- Enable: to give someone the authority or means to do something (to cause to be able).
- Endanger: to put someone or something at risk (to cause to be in danger).
In the context of your crossword clues, the suggestion "cause to be" fits well with the prefix "en-," as both "enable" and "endanger" involve causing a change in state or condition.