….that duct tape is excellent for everything with the exception of ducts, which require foil tape or mastic?
I read that duct tape was developed during WWII for sealing ammo boxes.
This question leads to others, even more difficult (like why do we park on a drive-way and drive on a park-way?). Let’s not even go there.
27th Street 
Perhaps that is why people increasingly refer to it as”duck” tape rather than “duct” tape. Over here in certain circles, we call it “gaffer tape” because of its wide application by stage crews – “gaffer” was usually a word used to refer to “the boss” who was in charge of the crew, but now it has become a verb in its own right, “why don’t we just gaffer it down”. I have been told that the king of all duct/gaffer/duck tapes is, in fact, called “gorilla” tape … go figure …
Duck and Gorilla are both brands. The Gorilla people also make awesome glue and I can attest that their “Gorilla” tape (which is black) is great stuff. It is thicker than ordinary duct tape and it kind of molds down to whatever you’re taping. I’ve used it outside with some success.