The most common and most likely answer to this crossword clue is the 11 letter word COEXTENSIVE
I've seen this crossword clue in The Times
C
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Buddy explains!
The straight part
We know that "covering same length" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case covering same length = coextensive.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 COEXTENSIVE mean?
COEXTENSIVE adjective- Having the same spatial limits or boundaries; sharing the same area.
- Occurring over the same period of time; contemporaneous.
- Having the same extension—the object or set of objects to which a term refers.