"J. Clarke" fired this volley in
in.local:

But if you look into the history of it, it appears that "duct" is the
actual corruption. It was originally a tape with a backing of a type
of
fabric called "duck", and was used for sealing ammunition cans, not
HVAC
ducts.

There was a very early tape made from duck. It was "floppy" and
flexible, and did well working over extremely uneven surfaces.

But there also a formally-called "duct tape" made from canvas, not duck,
and very stiff -- designed to seal the gaps in uniformly-sized pipes...

LLoyd