(of a voice or sound) That resembles the quack of a duck.
Fraudulent; characterised by or using the methods of quackery.
1998 September 9, Joni Mitchell, interview quoted in 2003, Alan Hecht, Polio, page 72,
I know this sounds real quacky but they did some mysterious good to the problem and I feel fine.
(US, of land or a crop) Infested with quackgrass.
1859, The Cultivator, Volume 7, 3rd Series, page 54,
After the first hoeing of a quacky crop, it is often well to go over it lightly in the middle of a hot day, just skimming the surface of the soil, and cutting off the young grass.
1914, New York (State) Department of Agriculture, Annual Report, Volume 1, Part 2, page 544,
When would you advise plowing sandy soil that is quacky for beans?