The most common and most likely answer to this crossword clue is the 11 letter word MASTERMINDS
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Buddy explains!
The straight part
We know that "planners" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case planners = masterminds.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 MASTERMINDS mean?
MASTERMINDS noun- A person with an extraordinary intellect or skill that is markedly superior to his or her peers.
- A person responsible for the highest level of planning and execution of a major operation.
- To act in the role of mastermind.