To use Office Home & Student 2013 RT in a commercial setting, it must be tied to another Office license that is.

"Organizations who purchase commercial use rights or have a commercial license to Office 2013 suites can use Office Home & Student 2013 RT for commercial, nonprofit, or revenue-generating activities," Microsoft explained in a statement, and in an FAQ on the company's website that was revised Wednesday.

ZDNet blogger and longtime Windows watcher first reported on the fine print.

Those rights can be acquired through some of the upcoming Office 365 subscriptions aimed at businesses -- which for a flat yearly fee let a worker run Office 2013 on up to five different devices -- by purchasing a higher-priced perpetual-licensed copy of Office Standard 2013 or Office 2013 Professional Plus; or by having an Office volume licensing contract, such as the annuity-like Software Assurance, in place.

In other words, to use Office Home & Student 2013 RT on a Windows RT tablet, businesses must have another, corporate-class license in place for the employee, even if the device is owned by that worker.