The most common and most likely answer to this crossword clue is the 6 plus 7 letter word BEETLE CRUSHER
I've seen this crossword clue in Financial Times
B
E
E
T
L
E
C
R
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H
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More clues leading to the result BEETLE CRUSHER
Buddy explains!
The straight part
We know that "large boot" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case large boot = beetle crusher.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 BEETLE CRUSHER mean?
BEETLE CRUSHER noun- A large, flat foot