The most common and most likely answer to this crossword clue is the 5 letter word WANES
I've seen this crossword clue in The Guardian
W
A
N
E
S
Buddy explains!
The straight part
We know that "peters out" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case peters out = wanes.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 WANES mean?
WANES noun- A gradual diminution in power, value, intensity etc.
- The lunar phase during which the sun seems to illuminate less of the moon as its sunlit area becomes progressively smaller as visible from Earth.
- The end of a period.
- A rounded corner caused by lack of wood, often showing bark.
- To progressively lose its splendor, value, ardor, power, intensity etc.; to decline.
- Said of light that dims or diminishes in strength.
- Said of the Moon as it passes through the phases of its monthly cycle where its surface is less and less visible.
- Said of a time period that comes to an end.
- To decrease physically in size, amount, numbers or surface.
- To cause to decrease.
- A child.
- A house or dwelling.