Strictly speaking ARM hasn't stood for anything since 1998 or so when it rebranded itself as part of going public (before which it had a period of being Advance

Strictly speaking ARM hasn't stood for anything since 1998 or so when it rebranded itself as part of going public (before which it had a period of being Advanced RISC Machines, though it did start as Acorn RISC Machines). Indeed it's now "Arm" and not an initialism at all...