The most common and most likely answer to this crossword clue is the 7 letter word POST-IT
I've seen this crossword clue in The Guardian
P
O
S
T
-
I
T
More clues leading to the result POST-IT
Buddy explains!
The straight part
We know that "Brief note" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case brief note = post-it.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 POST-IT mean?
POST-IT noun- A post-it note.