The most common and most likely answer to this crossword clue is the 12 letter word CONSTRUCTION
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More clues leading to the result CONSTRUCTION
Buddy explains!

The straight part
We know that "establishment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case establishment = construction.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 CONSTRUCTION mean?
CONSTRUCTION noun- The process of constructing.
- Anything that has been constructed.
- The trade of building structures.
- A building, model or some other structure.
- A (usually non-representational) structure, such as a collage etc.
- The manner in which something is built.
- (grammar) A group of words arranged to form a meaningful phrase.
- The act or result of construing the meaning of something.
- The meaning or interpretation of a text, action etc.; the way something is viewed by an observer or onlooker.
- A geometric figure of arcs and line segments that is drawable with a straightedge and compass.