The most common and most likely answer to this crossword clue is the 7 letter word PRUDENT
I've seen this crossword clue in The Daily Telegraph
P
R
U
D
E
N
T
More clues leading to the result PRUDENT
- Discreet page fronts filthy book collection
- Careful study, engaged in quiet routine
- Cautious piano tuner perturbed about key
- Puritan heartless, not cautious
- Wise one who’s easily offended by National Trust
- Discreet priest with dirty religious books
- Careful having to write about endlessly vulgar time
- Well-judged page introducing offensive section of scripture
- Wise, quiet, like Gray’s forefathers. going by the books
- Pastor disrespectful, not wise
Buddy explains!

The straight part
We know that "Discreet" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case discreet = prudent.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 PRUDENT mean?
PRUDENT adjective- Sagacious in adapting means to ends; circumspect in action, or in determining any line of conduct; careful, discreet, sensible; — opposed to rash; directed by prudence or wise forethought; evincing prudence
- Practically wise, judicious, shrewd
- Frugal; economical; not extravagant;