The most common and most likely answer to this crossword clue is the 7 letter word MOORHEN
M
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R
H
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N
More clues leading to the result MOORHEN
- Lake bird ultimately happier on home ground
- Bird or chap seen during the day
- Low layer attached to end of altar rail
- Second injured heron or other waterbird
- Disturbed hormone making one grouse
- Bird has hormone disorder
- Flier to secure ambassador's number
- Heron, distracted, following second waterbird
- Give a cheeky display around republican diplomat and flapper
Buddy explains!

The straight part
We know that "waterbird" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case waterbird = moorhen.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 MOORHEN mean?
MOORHEN noun- Any of various medium-sized water birds of the genus Gallinula, of the rail family, that feed in open water margins.
- A female red grouse, Lagopus lagopus scotica.