The most common and most likely answer to this crossword clue is the 6 letter word LUNULA
L
U
N
U
L
A
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The straight part
We know that "zone of 11Dn." is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case zone of 11dn. = lunula.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 LUNULA mean?
LUNULA noun- Something shaped like a crescent or half-moon; especially the pale area at the base of the fingernail.