The most common and most likely answer to this crossword clue is the 7 letter word CASSIUS
I've seen this crossword clue in The Times
C
A
S
S
I
U
S
More clues leading to the result CASSIUS
- Conservative idiot is hanging around university, a plotter
- One who conspired with accountants originally installed in S America
- Clay, perhaps, brought by small spades into college
- Cambridge college admitting sons of old assassin
- Person behind conspiracy to kill Caesar and an old Pope held by secret police? Quite the contrary
Buddy explains!
The straight part
We know that "One who conspired" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one who conspired = cassius.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.