The most common and most likely answer to this crossword clue is the 12 letter word OVERPOWERING
I've seen this crossword clue in Financial Times
O
V
E
R
P
O
W
E
R
I
N
G
Buddy explains!

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 OVERPOWERING mean?
OVERPOWERING verb- To subdue someone by superior force.
- To excel or exceed in power; to cause to yield; to subdue.
- To render imperceptible by means of greater strength, intensity etc.
- To make excessively powerful.
- That overpowers; so strong as to be overwhelming.