The most common and most likely answer to this crossword clue is the 7 plus 3 plus 5 letter word CHAPTER AND VERSE
I've seen this crossword clue in Financial Times
C
H
A
P
T
E
R
A
N
D
V
E
R
S
E
More clues leading to the result CHAPTER AND VERSE
- Local branch hostile about new detailed references
- Precise reference cathedral clergy note in poetry of our era?
- Reverend sat uneasily after fellow's precise testimony
- Exact reference prevents charade in development
- Branch badly served by an exact authority
- What makes CV an authoritative source
- Advent: preachers disposed to give one this?
- Servant preached, possibly giving one this?
- Fellow revised NT, reserved a location for text
- In other words, prevented a crash, given all the sources of evidence
Buddy explains!
The straight part
We know that "exact authority" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case exact authority = chapter and verse.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.