The most common and most likely answer to this crossword clue is the 8 letter word SATANISM
I've seen this crossword clue in Financial Times
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Buddy explains!
The straight part
We know that "form of worship" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case form of worship = satanism.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 SATANISM mean?
SATANISM noun- Worship of Satan (usually synonymous with "the Devil").
- A profession, philosophy, or ideological construct featuring a positive, admirable, or useful association to the figure, character or entity known as 'Satan'; or, featuring opposition to all morality and the procurement of what is wanted regardless of the consequences concerning others.
- LaVeyan Satanism.
- A devilish disposition.