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.