The "RT" In Windows RT has no official meaning according to Microsoft but there is a general use that suggests its origins.
RT does stand for Runtime, which has been in long time use - long before Windows 8 - so it is natural to think there was some sort of natural progression internally at Microsoft from the early days of referencing Runtime to a shorted form of RT to WinRT to the current naming of WindowsRT.
To confuse matters more, WinRT is the formal name of the APIs used to develop Windows 8 apps and programs, as in WinRT APIs (not WindowsRT!). These APIs let developers code once for programs that would work on both the ARM processor-based and Intel processor-based versions of Windows 8.
So WinRT does not directly translate to WindowsRT or vice-versa - there is just a hint of meaning referencing each other.
It could also be a clever play on "real-time" meaning the operating system is for light-weight OSes running on phones and tablets, but once again, this is not an official naming.
Dale Janssen is a co-founder of Techopedia and has been involved in the IT Industry for most of his career. He purchased his first computer in 1978 - an Ohio Scientific computer with a whopping memory size of 48K, operating a relic of an operating system called CPM. In fact, his roots go so far back in the computing biz that when he graduated from university, there was no such thing as a computer science department. 
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