The most common and most likely answer to this crossword clue is the 8 letter word RELIGION
I've seen this crossword clue in The Sunday Telegraph
R
E
L
I
G
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N
More clues leading to the result RELIGION
- Faith is what’s central to belief covered by tract
- District in which priest supplants eastern system of belief
- Area embracing state’s belief system
- Faith in generalissimos restored after purging rebellious masses
- Tract contains essence of belief giving faith
- Faith in inexperienced driver one follows, in part
- Belief about brave man, soldier imprisoned
- More than fifty will get access to area code
- One girl I converted to the faith
- Faith is one girl I fancy
Buddy explains!

The straight part
We know that "Faith" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case faith = religion.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 RELIGION mean?
RELIGION noun- Belief in a spiritual or metaphysical reality (often including at least one deity), accompanied by practices or rituals pertaining to the belief.
- A particular system of such belief, and the rituals and practices proper to it.
- The way of life committed to by monks and nuns.
- Rituals and actions associated with religious beliefs, but considered apart from them.
- Any practice to which someone or some group is seriously devoted.
- Faithfulness to a given principle; conscientiousness.
- Engage in religious practice.
- Indoctrinate into a specific religion.
- To make sacred or symbolic; sanctify.