The most common and most likely answer to this crossword clue is the 11 letter word AFFIRMATIVE
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More clues leading to the result AFFIRMATIVE
Buddy explains!

The straight part
We know that "yes" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case yes = affirmative.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 AFFIRMATIVE mean?
AFFIRMATIVE noun- Yes; an answer that shows agreement or acceptance.
- (grammar) An answer that shows agreement or acceptance.
- An assertion.
- Pertaining to truth; asserting that something is; affirming
- Pertaining to any assertion or active confirmation that favors a particular result
- Positive
- Confirmative; ratifying.
- Dogmatic
- Expressing the agreement of the two terms of a proposition.
- Positive; not negative
- An elaborate synonym for the word yes.
- (especially radio communications) Yes; true; correct.