Cryptic crossword clue
This difficult sum recalled Panama, perhaps 7

The most common and most likely answer to this crossword clue is the 7 letter word ISTHMUS

I've seen this crossword clue in The Guardian
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Buddy explains!

The straight part
We know that "Panama, perhaps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case panama, perhaps = isthmus.
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 ISTHMUS mean?

ISTHMUS noun
  1. A narrow strip of land, bordered on both sides by water, and connecting two larger landmasses.
  2. Any such narrow part connecting two larger structures.
  3. An edge in a graph whose deletion increases the number of connected components of the graph.

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