The most common and most likely answer to this crossword clue is the 3 letter word ISM
I've seen this crossword clue in The Times
I
S
M
More clues leading to the result ISM
- Unspecified doctrine originally inspiring so many
- Left-wingers for instance spouting Marxist doctrine
- Set of beliefs is followed by millions
- This author’s taking in singular theory
- Practice enabling one to take lead in computer game
- Man needing a change of heart and belief
- Distinctive theory is mathematician’s first
- Theory exists with maths, at first
- Doctrine remains with Magdalen's principal
- Ideology is mesmerising at first
Buddy explains!
The straight part
We know that "Set of beliefs" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case set of beliefs = ism.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 ISM mean?
ISM noun- An ideology, system of thought, or practice that can be described by a word ending in -ism.
- Specifically, a form of discrimination, such as racism or sexism.