The most common and most likely answer to this crossword clue is the 3 plus 7 letter word WET BLANKET
I've seen this crossword clue in The Guardian
W
E
T
B
L
A
N
K
E
T
More clues leading to the result WET BLANKET
- I'm no fun, as a result of sweaty night?
- Spoiler of fun is clear in unfortunate tweet
- Have accident in bed? No joy for him
- Possible result of sleeping outdoors? Misery!
- Misery, western and Aliens — nothing between them
- Killjoy in battle knew to yield
- Spoilsport being vacuous in silly tweet
- Killjoy melting snow could be described as such
- Dreary pessimist knew battle is lost
- With void between two spacemen, there’s misery
Buddy explains!
The straight part
We know that "Killjoy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case killjoy = wet blanket.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 WET BLANKET mean?
WET BLANKET verb- To disparage, belittle, or remove the satisfaction and joy from; to act as a wet blanket towards.