The most common and most likely answer to this crossword clue is the 6 letter word RECAPS
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The straight part
We know that "sums up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sums up = recaps.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 RECAPS mean?
RECAPS noun- A tire that has had new tread glued on.
- To seal (something) again with a cap.
- To replace the worn tread on a tire by gluing a new outer portion. (US English only - Retread in UK English)
- A recapitulation.
- To recapitulate.
- A leveraged recapitalization accomplished by increasing the debt to equity ratio.
- To replace capacitors in electronic equipment.