Comment by eesmith

Yes.

The 1966 book "Computer dictionary and handbook" mentions many appropriate uses, like GECOS, the GEneral Comprehensive Operating System. https://archive.org/details/computerdictiona0000unse/page/64...

UNIX is a play on MULTICS, an earlier time-sharing operating system.

The 1965 MULTICS paper at https://www.multicians.org/fjcc1.html has "it is an obligation to present and future system designers to make the inner operating system as lucid as possible so as to reveal the basic system issues" and cites ""IBM Operating System/360, PL/I: Language Specifications," File No. S360-29, Form C28-6571-1, I.B.M. Corp."

A 1968 manual for the IBM System/360 Disk Operating System is at https://bitsavers.org/pdf/ibm/360/dos/C24-3427-3_Disk_Operat... .