The most common and most likely answer to this crossword clue is the 5 letter word TANGA
I've seen this crossword clue in Financial Times
T
A
N
G
A
Buddy explains!

The straight part
We know that "briefs" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case briefs = tanga.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TANGA mean?
TANGA noun- Any of various former Asian coins, including: a coin of Portuguese India equal to 1/10th of a Rupee, a gold coin of India issued by various Muslim rulers, a silver coin of India, also issued by Muslim rulers, a former silver coin of Tibet.
- A bikini bottom composed of two triangular panels connected by strings at the side