The most common and most likely answer to this crossword clue is the 8 letter word SQUEALER
I've seen this crossword clue in Independent
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More clues leading to the result SQUEALER
Buddy explains!
The straight part
We know that "Rat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rat = squealer.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 SQUEALER mean?
SQUEALER noun- Any animal or person who squeals.
- A pig.
- An informant.
- Anything that makes a squealing noise.
- The European swift.
- The harlequin duck.
- The American golden plover.
- A young pigeon.