The most common and most likely answer to this crossword clue is the 8 letter word FABULOUS
I've seen this crossword clue in The Times
F
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Buddy explains!

The straight part
We know that "Wonderful" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wonderful = fabulous.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 FABULOUS mean?
FABULOUS adjective- Of or relating to fable, myth or legend.
- Characteristic of fables; marvelous, extraordinary, incredible.
- Fictional or not believable; made up.
- Known for telling fables or falsehoods; unreliable.
- Very good; outstanding, wonderful.
- Gay or pertaining to gay people.
- Camp, effeminate.
- Fashionable, glamorous