The most common and most likely answer to this crossword clue is the 11 letter word SUPER-DUPER
S
U
P
E
R
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D
U
P
E
R
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 SUPER-DUPER mean?
SUPER-DUPER adjective- Very excellent; truly great.
- Complete, total, absolute.