The most common and most likely answer to this crossword clue is the 6 letter word LEAPED
L
E
A
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Buddy explains!

The straight part
We know that "Negotiated" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case negotiated = leaped.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 LEAPED mean?
LEAPED verb- To jump.
- To pass over by a leap or jump.
- To copulate with (a female beast); to cover.
- To cause to leap.