The most common and most likely answer to this crossword clue is the 6 letter word PEEWEE
I've seen this crossword clue in Financial Times
P
E
E
W
E
E
Buddy explains!

The straight part
We know that "Singer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case singer = peewee.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 PEEWEE mean?
PEEWEE noun- A short or small person; a small object.
- A kind of small marble in children's games.
- A player in a sports league for very young children.
- (New South Wales and Queensland) A magpie-lark or mudlark, Grallina cyanoleuca.
- A pewee.