As an aside, I'd always been under the impression that the "AB" in "ABEND" comes from, "abnormal"?
That was what taught when I was hacking on TSS/360 (before I even saw UNIX). The term was used in the IBM batch system to say your job died or stopped with an abnormal ending (i.e. The job returned exit(NONZEROVALUE) to the OS in UNIX terms [or the OS killed it for some reason and forced it to exit in that manner].
As for Richard's question about abort(), no idea. I had heard the term used to kill off an errant process/job/task used in other systems before I ever came to Unix. You'd probably need some like Doug M or Knuth that goes back far enought to help you with history.