The most common and most likely answer to this crossword clue is the 9 letter word TURNSTONE
I've seen this crossword clue in Financial Times
T
U
R
N
S
T
O
N
E
Buddy explains!
The straight part
We know that "Wader" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wader = turnstone.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 TURNSTONE mean?
TURNSTONE noun- Either of two species of coastal wading bird, Arenaria interpres and Arenaria melanocephala, that breed in the Arctic and readily turn stones or seaweed looking for hidden invertebrates.