The most common and most likely answer to this crossword clue is the 10 letter word ISOMORPHIC
I've seen this crossword clue in The Guardian
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More clues leading to the result ISOMORPHIC
Buddy explains!

The straight part
We know that "in same structure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in same structure = isomorphic.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 ISOMORPHIC mean?
ISOMORPHIC adjective- Related by an isomorphism; having a structure-preserving one-to-one correspondence.
- Having a similar structure or function to something that is not related genetically or through evolution.
- Having identical relevant structure; being structure-preserving while undergoing certain invertible transformations.