The most common and most likely answer to this crossword clue is the 4 letter word MARL
I've seen this crossword clue in Financial Times
M
A
R
L
More clues leading to the result MARL
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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 MARL mean?
MARL noun- A mixed earthy substance, consisting of carbonate of lime, clay, and possibly sand, in very variable proportions, and accordingly designated as calcareous, clayey, or sandy.
- To cover with the earthy substance called marl.
- To cover, as part of a rope, with marline, marking a peculiar hitch at each turn to prevent unwinding.