The most common and most likely answer to this crossword clue is the 11 letter word SUBJUNCTIVE
I've seen this crossword clue in The Times
S
U
B
J
U
N
C
T
I
V
E
Buddy explains!
The straight part
We know that "a doubtful mood" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a doubtful mood = subjunctive.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 SUBJUNCTIVE mean?
SUBJUNCTIVE noun- A form in the subjunctive mood.
- (grammar, of a verb) Inflected to indicate that an act or state of being is possible, contingent or hypothetical, and not a fact.
- (grammar) Mood expressing an action or state which is hypothetical or anticipated rather than actual, including wishes and commands.