The most common and most likely answer to this crossword clue is the 8 letter word EMISSARY
I've seen this crossword clue in The Daily Telegraph
E
M
I
S
S
A
R
Y
More clues leading to the result EMISSARY
- Careless king dropping a line, one dispatched officially
- English girl: a railway representative
- English teacher cautious in absence of head delegate
- English girl fairly regularly visited diplomat
- Eastern girl: a railway agent
- Envoy from Middle East backed Syria’s reforming
- Envoy from Elizabeth bestowing title on beheaded Scottish queen
- Representative from record company’s claim about Queen
- Wasted year framing young female agent
- Single female in troubled year as agent
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 = emissary.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 EMISSARY mean?
EMISSARY noun- An agent sent on a mission to represent the interests of someone else.
- A venous channel in the skull.
- An underground channel by which the water of a lake escapes.