The most common and most likely answer to this crossword clue is the 9 letter word PLIMSOLES
P
L
I
M
S
O
L
E
S
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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 PLIMSOLES mean?
PLIMSOLES noun- A rubber-soled lace-up canvas shoe for sports or onboard ships; a precursor of trainers.
- The plimsoll symbol ⦵ (or o) that is used as a superscript in the notation of thermodynamics to indicate an arbitrarily chosen non-zero reference point.