The most common and most likely answer to this crossword clue is the 7 letter word TANAGER
I've seen this crossword clue in The Times
T
A
N
A
G
E
R
Buddy explains!

The straight part
We know that "American singer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case american singer = tanager.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 TANAGER mean?
TANAGER noun- Any of numerous species of often colorful passerine birds that inhabit New World forests, formerly all within the family Thraupidae, but now with some species placed in other families with birds such as finches and cardinals.