The most common and most likely answer to this crossword clue is the 8 letter word AMBIENCE
I've seen this crossword clue in The Guardian
A
M
B
I
E
N
C
E
More clues leading to the result AMBIENCE
- A doctor in church nurses European character
- Mood displayed by a doctor having treated niece
- Bishop’s put in appearance, impressed by excellent atmosphere
- Atmosphere in heart of mine became explosive
- Atmosphere changed in empty Berkshire cinema
- Book set in abandoned mine described with great atmosphere
- Boron in air supplements cool atmosphere
- Beam with nice well-disposed feeling
- Aura coming from a bishop through presence at church
- Be manic, excited consuming ecstasy and spirit
Buddy explains!

The straight part
We know that "mood" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mood = ambience.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 AMBIENCE mean?
AMBIENCE noun- A particular mood or atmosphere of an environment or surrounding influence.
- (3D models) A secondary color of a polygon that becomes more pronounced with shading.