* regula: This is a good general term for a "rule," often referring to a guiding principle or a prescribed method. Think of it like a "ruler" or a "rule of thumb."
* ius: This translates more to "law" or "right," and would be appropriate if the "rule" is a legal or established principle.
* lex: Similar to "ius," this refers to a "law" or statute.
* imperium: This signifies "command," "authority," or "power" and would be suitable if the "rule" is exercised by someone in a position of authority.
* potestas: This means "power" or "authority," and works well when referring to the power to rule.
To choose the best word, consider what kind of "rule" you're referring to. For example:
* "The rule of law" would be *ius*.
* "A grammar rule" might be *regula*.
* "The king's rule" would likely be *imperium* or *potestas*.
Therefore, there's no single answer; the best translation needs context.