The most common and most likely answer to this crossword clue is the 4 letter word SURE
S
U
R
E
More clues leading to the result SURE
- Firm runs through claim in court
- Trim, having lost weightwithout a doubt
- Confident Republican in to take action
- Sound of the seaside? Yes!
- Entice with first of sweeteners for Liberal to make certain
- Girl keeps king safe
- Doubtless, it follows plea for enjoyment
- Safe old city in Home Counties
- Stable bank, by the sound of it
- Yes, sack is reliable
Buddy explains!

The straight part
We know that "without a doubt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case without a doubt = sure.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 SURE mean?
SURE adjective- Physically secure and certain, non-failing, reliable.
- Certain in one's knowledge or belief.
- Certain to act or be a specified way.
- Free from danger; safe; secure.
- Betrothed; engaged to marry.
- (modal adverb) Without doubt, certainly.
- Yes. (Expresses noncommittal agreement or consent.)
- Yes; of course.