The most common and most likely answer to this crossword clue is the 12 letter word STRANGLEHOLD
I've seen this crossword clue in Financial Times
S
T
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A
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D
More clues leading to the result STRANGLEHOLD
- Grip left in odd storage space on ship
- Most of the Lords excited about scheme – it’s breathtaking
- Unusually long halters on donkeys at the front giving complete control
- Clamp left in odd place in ship
- A firm grip on the throttle?
- She’ll not drag out, there’s a tight grip!
- Grand to shell out for total control
- Alien chokes large bear in illegal wrestling move
- Curious about line judge in complete control
Buddy explains!

The straight part
We know that "complete control" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case complete control = stranglehold.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 STRANGLEHOLD mean?
STRANGLEHOLD noun- A grip or control so strong as to stifle or cut off.
- To hold a tight grip or control