The most common and most likely answer to this crossword clue is the 7 letter word FRACTAL
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More clues leading to the result FRACTAL
Buddy explains!

The straight part
We know that "Pattern" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pattern = fractal.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 FRACTAL mean?
FRACTAL noun- A mathematical set that has a non-integer and constant Hausdorff dimension; a geometric figure that is self-similar at all scales.
- An object, system, or idea that exhibits a fractal-like property.
- Having the form of a fractal.
- Exhibiting a fractal-like property.
- Having a broken part