The most common and most likely answer to this crossword clue is the 12 letter word CONTERMINOUS
I've seen this crossword clue in Independent
C
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Buddy explains!

The straight part
We know that "without a break" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case without a break = conterminous.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.
Crossword Answer definitions
CONTERMINOUS adjective- Meeting end to end or at the ends.
- Having matching boundaries; or, adjoining and sharing a boundary.
- Having the same scope, range of meaning, or extent in time.
- Said of linked or related property leases that expire together.