The most common and most likely answer to this crossword clue is the 4 letter word GURU
I've seen this crossword clue in The Times
G
U
R
U
More clues leading to the result GURU
- Master some sticky matter — regret speaking out
- Floor covering turned over by university teacher
- Teacher in toupee rejected by university
- Soviet spies arresting university teacher
- Expert tip for learning language in Asia, not Germany
- Spiritual guide misinterpreted augury’s contents
- Teacher in wig, retired by university
- Expert hears W almost breaking into G&R
- Teacher’s turning over carpet with a bit of underfelt
- Leader took viol round ancient city
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 = guru.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 GURU mean?
GURU noun- A Hindu or Sikh spiritual teacher.
- (sometimes humorous) An influential advisor or mentor.