The most common and most likely answer to this crossword clue is the 8 letter word GRIPPING
I've seen this crossword clue in The Guardian
G
R
I
P
P
I
N
G
More clues leading to the result GRIPPING
Buddy explains!

The straight part
We know that "riveting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case riveting = gripping.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 GRIPPING mean?
GRIPPING verb- To take hold of, particularly with the hand.
- To help or assist, particularly in an emotional sense.
- To do something with another that makes you happy/gives you relief.
- To trench; to drain.
- Pinching and spasmodic pain in the intestines; gripe.
- Which catches someone's attention; exciting