The most common and most likely answer to this crossword clue is the 5 letter word NAPPE
N
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P
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The straight part
We know that "sheet of sums?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sheet of sums? = nappe.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 NAPPE mean?
NAPPE noun- The profile of a body of water flowing over an obstruction in a vertical drop.
- Either of the two parts of a double cone.
- A sheet-like mass of rock that has been folded over adjacent strata.
- (hydraulics) Geological nappe whose underside is not in contact with the overflow structure and is at ambient atmospheric pressure.
- The ability of a liquid to coat the back of a spoon, etc.
- To coat (a food) with liquid.