Doohickey, etc.

[Jim McKee]

Hi everyone - growing up in the 50's in NE Central Mississippi, I heard
"doohickey" used often to equate roughly to "gizmo" and to refer to
unknown devices, e.g. "What do you call that little doohickey on the top
of the pressure cooker?" (Incidentally, "petcock" sounds even sillier
than "doohickey" to me!).
I also heard "doomaflotchy" used either as "doohickey" was or to refer
to an unknown person, e.g. "You know, Mrs. Doomaflotchy that works at
the courthouse!"
I think I heard "doohickey" nationally, probably on the radio.
Does anyone know if these terms have an origin in some national
language?  Or, they could have become popular as "bromide" did from
Burgess or one of the other widely popular humorists.

Jim