The most common and most likely answer to this crossword clue is the 5 letter word HINDU
I've seen this crossword clue in The Times
H
I
N
D
U
More clues leading to the result HINDU
- A believer in hi-tech industry
- Brahmin, possibly, contributing to growth industry
- Indian perhaps back with uniform
- Believer from Nazareth in dungeon
- Indian delivering part of speech in Dutch
- Worshipper for whom church in Dudley providing sanctuary
- Believer pulled from filth in dungeon
- Religion is a bit of a growth industry
- One who has faith in house God destroyed, sacrificing goose
- She’s forbidden to eat cow, deer and sheep, reportedly
Buddy explains!

The straight part
We know that "A believer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a believer = hindu.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.