Length/Duration:
* Long: This is the most common opposite, referring to something that lasts a significant amount of time.
* Extended: Similar to long, but implying a specific stretching out of time.
* Protracted: Suggesting a long and drawn-out process.
Details/Content:
* Comprehensive: Meaning covering everything in detail.
* Detailed: Providing a lot of information.
* Extensive: Having a wide scope or range.
* Elaborate: Giving a lot of specific information or explanation.
Concise/Clear:
* Rambling: Lacking focus and direction, going off on tangents.
* Verbose: Using more words than necessary, being wordy.
* Vague: Lacking clarity and specific details.
Informal/Informal:
* Formal: Structured and adhering to a strict protocol.
* Detailed: Offering a lot of specific information.
To give you the most accurate opposite, please provide me with the specific context in which you are using the word "brief".