"Clear" as a synonym:
* For understandable: Yes, "clear" is a synonym for "understandable" or "intelligible." For example: "The instructions were clear."
* For visible: Yes, "clear" is a synonym for "visible" or "transparent." For example: "The water was clear."
* For empty: Yes, "clear" can be a synonym for "empty," but it's usually used in a more specific sense, like "clear the table" or "clear the air."
"Clear" as NOT a synonym:
* For "bright": While "clear" can imply brightness, it's not a synonym. You wouldn't say "The sun is clear" when you mean "The sun is bright."
To determine if "clear" is a synonym in a particular context, think about what you want to say and consider the other words that might be used to convey the same meaning.