The most common and most likely answer to this crossword clue is the 9 letter word MOONLIGHT
I've seen this crossword clue in The Sunday Telegraph
M
O
O
N
L
I
G
H
T
More clues leading to the result MOONLIGHT
- Spooner’s Canadian diver could possibly have a second job
- Perform other work, a piece for piano
- Film work on a second job
- Hang about, solution is 8
- Low luminance in the dark?
- Low thing possibly to hoard pounds and work illegally
- Sonata form of flit?
- Hint: gloom transformed by this?
- Illumination that could be low level initially in time of darkness
- Spooner’s idiot may take on extra duty?
Buddy explains!

The straight part
We know that "this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this = moonlight.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 MOONLIGHT mean?
MOONLIGHT noun- (sometimes attributive) The light reflected from the Moon.
- To work on the side (at a secondary job), often in the evening or during the night.
- (by extension) To engage in an activity other than what one is known for.
- (by extension, of an inanimate object) To perform a secondary function substantially different from its supposed primary function, as in protein moonlighting.
- To carry out undeclared work.