The Diablo 2 Wiki
The Diablo 2 Wiki archive is available for anyone looking for information on Diablo 2. All information here is pre-D2R but contains a lot of useful information that is still relevant. Updated sections for new D2R features can be found on the PureDiablo Diablo 2 section

Ethereal Runeword

From Diablo 2 Wiki

Yes, Ethereal RuneWords are possible, and no, it's not a real good idea to make one, unless you are doing it specifically for your merc to use.