Cryptic crossword clue
Shade under a hundred standard rings of a particular shape 11

The most common and most likely answer to this crossword clue is the 11 letter word RECTANGULAR

I've seen this crossword clue in Financial Times
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Buddy explains!

The straight part
We know that " /of a particular shape" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case  /of a particular shape = rectangular.
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 RECTANGULAR mean?

RECTANGULAR adjective
  1. Having a shape like a rectangle.
  2. Having axes that meet each other with right angles.

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