The most common and most likely answer to this crossword clue is the 7 letter word MALLARD
I've seen this crossword clue in Independent
M
A
L
L
A
R
D
More clues leading to the result MALLARD
- Loco dabbler?
- Mother with large, fat duck
- Duck fat on drake, perhaps, endless
- A couple of lines in short play about record-breaker
- Duck taken from arcade – charge wife denied
- Doctor eating every last bit, given a recipe for duck
- Shopping arcade – one by river, deserted
- Mussels and lychees for starters at The Fat Duck?
- Menu’s starter – a large fat duck
- Man practically fronting Fat Duck
Buddy explains!

The straight part
We know that "record-breaker" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case record-breaker = mallard.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 MALLARD mean?
MALLARD noun- A common and widespread dabbling duck, Anas platyrhynchos, whose male has a distinctive dark green head.