The most common and most likely answer to this crossword clue is the 6 letter word PHONEY
P
H
O
N
E
Y
More clues leading to the result PHONEY
- False subject of litmus test over twelve month period
- Quiet sweetheart may be a hypocrite
- Fake ring — the ultimate in chicanery
- Call by made by unknown character – one attempting a scam?
- Counterfeit currency Miles left behind pub
- Fake ring revealed by youth leader
- With fake ring, marry at last
- Soft term of endearment is insincere
- Impostor such as a ringer
- Poultry keeping tip: ducks quack
Buddy explains!

The straight part
We know that "quack" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case quack = phoney.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 PHONEY mean?
PHONEY noun- A person who assumes an identity or quality other than their own.
- A person who professes beliefs or opinions that they do not hold.
- Anything fraudulent or fake.
- Fraudulent; fake; having a misleading appearance.