The most common and most likely answer to this crossword clue is the 8 letter word CATALYST
I've seen this crossword clue in The Guardian
C
A
T
A
L
Y
S
T
More clues leading to the result CATALYST
- Promoter of change, one leaving country in company of actors
- Agent who changes players going round country with no capital
- Agent of change given role encompassing country short of capital
- Agent changes last act around the 4th of July
- About time a series of items is mentioned – that should expedite things
- Reckoning to forget one line when amongst actors? This encourages change
- Whip: “Lay off senior Tory leaders!” which makes a change
- Agent taking one pound from sum received by actors
- Tom, say, getting a set of items, we hear — engineer of change?
Buddy explains!
The straight part
We know that "Agent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case agent = catalyst.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 CATALYST mean?
CATALYST noun- A substance that increases the rate of a chemical reaction without being consumed in the process.
- Someone or something that encourages progress or change.
- An inciting incident that sets the successive conflict into motion.
- A catalytic converter.