The most common and most likely answer to this crossword clue is the 13 letter word INCORPORATION
I've seen this crossword clue in The Times
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Buddy explains!
The straight part
We know that "merger" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case merger = incorporation.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 INCORPORATION mean?
INCORPORATION noun- The act of incorporating, or the state of being incorporated.
- The union of different ingredients in one mass; mixture; combination; synthesis.
- The union of something with a body already existing; association; intimate union; assimilation
- The act of creating a corporation.
- A body incorporated; a corporation.
- A phenomenon by which a grammatical category forms a compound with its direct object or adverbial modifier, while retaining its original syntactic function.
- A doctrine of constitutional law according to which certain parts of the Bill of Rights are extended to bind individual American states. Wp