The most common and most likely answer to this crossword clue is the 8 letter word EDUCATOR
I've seen this crossword clue in The Guardian
E
D
U
C
A
T
O
R
More clues leading to the result EDUCATOR
- Carriage finally ahead of old silver and gold coach
- Teacher of English taking old coin
- Teacher finding old coin in excavation outside Rome originally
- School runner courted a disaster
- Sovereign inspiring couple to catch lion, say, for master
- Teacher mounted offensive, engaging censor once
- Academic turned dirty without censor
- Queen has invested old money on old coach
- Censor blocks the rise of blunt teacher
- Teacher raced out unexpectedly
Buddy explains!

The straight part
We know that "master" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case master = educator.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 EDUCATOR mean?
EDUCATOR noun- A person distinguished for his/her educational work, a teacher.