And with that little programming exercise, a second door cracked ajar. It was to swing wide open during the summer of 1969 when Thompson’s wife, Bonnie, spent a month visiting his parents to show off their newborn son. Thompson took advantage of his temporary bachelor existence to write a good chunk of what would become the Unix operating system for the discarded PDP‑7. The name Unix stems from a joke one of Thompson’s colleagues made: Because the new operating system supported only one user (Thompson), he saw it as an emasculated version of Multics and dubbed it “Un-multiplexed Information and Computing Service,” or Unics. The name later morphed into Unix.
“The Strange Birth and Long Life of Unix.” — Warren Toomey, IEEE Spectrum