Is it "Duck" tape or "Duct" tape?
The US Army during WW2 put out a spec for a waterproof tape that soldiers could use to seal plastic bags with their ammunition and supplies. The tape that was selected for the contract was made by Johnson and Johnson. The soldiers started calling it "Duck" tape since it was meant to keep out the water.
However, after the war HVAC contractors started using the stuff to seal duct work. Johnson and Johnson changed the color from Army Green to Sheet Grey, and thus "Duct" tape was born.
So, either is correct :D