The most common and most likely answer to this crossword clue is the 8 letter word BLINDING
I've seen this crossword clue in Financial Times
B
L
I
N
D
I
N
G
More clues leading to the result BLINDING
Buddy explains!

The straight part
We know that "excellent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case excellent = blinding.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 BLINDING mean?
BLINDING verb- To make temporarily or permanently blind.
- To curse.
- To darken; to obscure to the eye or understanding; to conceal.
- To cover with a thin coating of sand and fine gravel, for example a road newly paved, in order that the joints between the stones may be filled.
- The act of causing blindness.
- A thin coat of sand or gravel used to fill holes in a new road surface.
- A thin sprinkling of sand or chippings laid on a newly tarred surface.
- Very bright (as if to cause blindness).
- Making blind or as if blind; depriving of sight or of understanding.
- Brilliant; marvellous.
- To an extreme degree; blindingly.