The most common and most likely answer to this crossword clue is the 6 letter word SAY-SO
I've seen this crossword clue in Financial Times
S
A
Y
-
S
O
More clues leading to the result SAY-SO
- Consent expresses nothing
- Permission, for example, like that
- Authority stays tight-lipped?
- Authority that doesn’t speak?
- Verbal, but unwritten, authority
- Authority keeps quiet
- Authority to get broadcast?
- Approval from nosy assistant misdirected
- Final authority is Mum?
- Authority comes out with circular letter
Buddy explains!

The straight part
We know that "Permission" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case permission = say-so.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 SAY-SO mean?
SAY-SO noun- Authority, as backing some statement, injunction, or command.