Going back to Kat's original question. Almost anything seems fair to the xword mavens.
My wife- hopelessly hooked- used foreign language dictionaries, the complete Oxford, and slang dictionaries. Also the World Almanac, The Nat. Geographic Atlas and an old atlas from 1900 (the names do change), The Encyclopaedia Britannica- I could go on.

"Honey, would you look up a word for me?" always disrupts my Sundays. "One of these days, Alice," as Ralph Kramden said on The Honeymooners. "Pow! Right on the old kisser!"
   
To me, the worst are those which include the names of a lot of long dead philosophers, old book characters, and quotations from long-forgotten authors (Oh, yes, Bartlett's Quotations, mustn't forget that).