The most common and most likely answer to this crossword clue is the 5 letter word LEARN
I've seen this crossword clue in The Times
L
E
A
R
N
More clues leading to the result LEARN
- Understand king needing knight's backing
- Hear about tragic king meeting knight
- Digest litre — gross!
- English humorist with name to memorise
- Master driving pupil to achieve
- Discover tragic figure, forlorn at the last
- Receive knowledge from learner and bring home bacon?
- Study Latin at first and make money
- Commit to memory name of king, northern
- Pounds get paid to master
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 = learn.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 LEARN mean?
LEARN noun- The act of learning something
- To acquire, or attempt to acquire knowledge or an ability to do something.
- To attend a course or other educational activity.
- To gain knowledge from a bad experience so as to improve.
- To study.
- To come to know; to become informed of; to find out.
- To teach.