William Sommerwerck wrote:
Where in world did you come up with duck? One doesn't
tape ducks; one tapes ducts. Except it isn't very good for that...

So why the latter?

It might originally have been called duck tape. See the Etymology section of
the Wikipedia article.

http://en.wikipedia.org/wiki/Duct_tape

The issue is confusing, because it wasn't used for ducts until long after it
was invented.

Not so confusing now, as apparently there's a manufacturer of the stuff
with "Duck" in its name, putting out a product called
"'Duck Tape' brand of duct tape." Obviously in their interest to have
folks call it "Duck", but I've not run across this brand ever, but it
explains a whole lot.

--
john mcwilliams