The most common and most likely answer to this crossword clue is the 6 letter word SHINTO
I've seen this crossword clue in The Sunday Telegraph
S
H
I
N
T
O
More clues leading to the result SHINTO
- Quiet, and knowledgeable about ancient Japanese religion
- Quiet and enthusiastic about religion
- Thus penning clue for religion
- Accordingly including clue for traditional faith
- Faith very receptive to suggestion
- Mum, enthusiastic about religion
- Religion contributing to clash in Tokyo
- Say nothing enthusiastic about religion
- Secular humanist initially very appreciative of religion
- … religion thus riven by suspicion
Buddy explains!
The straight part
We know that "Eastern rel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case eastern rel = shinto.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.