We know that SIGABRT was once SIGIOT, which was what PDP-11 Unix reported
if the code executed an IOT instruction (which was all that abort() did).
IOT was a trap instruction used by the aboriginal PDP-11 Paper Tape
Software in order to communicate with device drivers.  Later DEC OSes used
EMT and Unix used TRAP, because the manual said it was for "user traps" and
Unix is a user operating system.  At some point it seemed stupid to someone
to call the user-level routine abort() and the signal SIGIOT, and so added
SIGABRT as a synonym.  Not really an answer, but that's all I have.

On Wed, Sep 1, 2021 at 10:24 AM Paul Winalski <paul.winalski@gmail.com>
wrote:

> On 9/1/21, Dan Cross <crossd@gmail.com> wrote:
> >
> > As an aside, I'd always been under the impression that the "AB" in
> "ABEND"
> > comes from, "abnormal"?
>
> You are correct, Dan.  ABEND comes from the IBM (specifically
> OS/360/370) world and is short for "abnormal end".  It means that
> application program (called the "problem program" in IBM mainframe
> jargon) has terminated abnormally for some reason and control has
> returned to the operating system.  An ABEND was typically followed by
> a core dump to the printer.  As the manual for beginning programmers
> at Boston College said, "Despite what your German teacher might tell
> you, there is no such thing as a guten ABEND."
>
> -Paul W.
>