The most common and most likely answer to this crossword clue is the 9 letter word CONFIDENT
I've seen this crossword clue in Financial Times
C
O
N
F
I
D
E
N
T
More clues leading to the result CONFIDENT
- Tory uncertainty brought about negative effect for sure
- Bold prisoner able to conceal hideaway
- Learn if getting over depression is optimistic
- Without a doubt, privately reveal name and model
- Sure trick provided to lift depression
- Sure about working if turning up with depression?
- Self-assured, able to absorb study after study
- Assured fine don works in college tutorials, principally
Buddy explains!

The straight part
We know that "sure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sure = confident.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 CONFIDENT mean?
CONFIDENT noun- A person in whom one can confide or share one's secrets: a friend.
- Very sure of something; positive.
- Self-assured, self-reliant, sure of oneself.
- (in negative sense) Forward, impudent.