Radio test : if some company will buy your domain Orchidios.com, and will want to use it in radio advertisement, they will say something like : please find more information about this company at WWW.Orchidios.com..and it will not pass radio test, because different people can pronounce this name differently, and radio listeners will not know exactly how the name is written, so it will be difficult for them to actually get to the website. This is bad for value of the domain name.
Your second name, NickMill.com, will pass radio test more likely, because when somebody will use it in radio advertisement, most people will know how to spell it, when they hear this name in radio, and they will be able to get to that website.
I hope it helped, cheers!
lolwarrior