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

The straight part
We know that "conspirator" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case conspirator = plotter.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 PLOTTER mean?
PLOTTER noun- A person who plots.
- An output device that draws graphs and other pictorial images on paper, sometimes using attached pens.
- An instrument used to mark or find the position of a vessel on a chart.
- To splash around in something wet; to dabble.
- To potter.