Earlier quoted context omitted.
And sometimes even parts of a trademark can be risky. https://en.wikipedia.org/wiki/Linspire
Unclear what you think that proves. Microsoft paid $20m to buy their trademark and they changed their name.
Yes, it went well for Linspire, still it attracted a lawsuit, and the reason they didn'tlose wasn't because Lindows is different from Windows but because "windows" was a generic term already used as such by Microsoft itself.
I wonder what would have happened if the MS product was called say WinOS and the other one LinOS, where none of the terms are common words so that similarity would be the only matter.