The most common and most likely answer to this crossword clue is the 6 letter word OCCULT
I've seen this crossword clue in The Daily Telegraph
O
C
C
U
L
T
More clues leading to the result OCCULT
- Magical old sect group outside college
- Potter’s second volume ultimately is magical
- Could mostly act deviously, unable to keep a secret
- Secret lock uncovered by sect
- Hidden sources of Conservative unrest welcomed by stupid clot
- Secret business, turning up at sect
- Cryptic clue almost solved in a month
- Officer in charge of sect dealing in the supernatural
- Nothing about religious sect is mysterious
- Hidden firm backing religious system
Buddy explains!

The straight part
We know that "Magi" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case magi = occult.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 OCCULT mean?
OCCULT noun- (usually with "the") Supernatural affairs.
- To cover or hide from view.
- To dissimulate, conceal, or obfuscate.
- Secret; hidden from general knowledge; undetected.
- Related to the occult; pertaining to mysticism, magic, or astrology.
- Esoteric.