Q:

Does referencing non-SRD material by name constitute "use"?

I am working on a homebrew deity book with the possibility of later publishing it. Having looked over the 5e SRD, the only cleric domain that is Open Content is the Life domain. It is nigh impossible to have a pantheon offering only one domain, and this leaves me in a bit of a quandary. I don't plan on including any mechanics, just saying that Zarth grants the Death domain (as an example). 
I don't believe that this constitutes "usage," but I would like to get some additional opinions before I go about publishing a book filled to the brim with that sort of thing.

A:

You might be able to get away with your specific case
I am not a lawyer, and I'm not qualified to give legal advice. However, reading the OGL, it looks like you're in a gray area: 

7.Use of Product Identity: You agree not to Use any Product Identity, including as an indication as to  compatibility, except as expressly licensed in  another, independent Agreement with the owner of  each element of that Product Identity. You agree not  to indicate compatibility or co-adaptability with any  Trademark or Registered Trademark in conjunction  with a work containing Open Game Content except  as expressly licensed in another, independent  Agreement with the owner of such Trademark or  Registered Trademark.  

What is product identity? A huge list of things: 

"Product Identity" means product and product line names, logos and identifying marks including trade dress; artifacts; creatures characters; stories, storylines, plots, thematic elements, dialogue, incidents, language, artwork, symbols, designs, depictions, likenesses, formats, poses, concepts, themes and graphic, photographic and other visual or audio representations; names and descriptions of characters, spells, enchantments, personalities, teams, personas, likenesses and special abilities; places, locations, environments, creatures, equipment, magical or supernatural abilities or effects, logos, symbols, or graphic designs;

A divine domain could arguably be one or more of the things described above (thematic elements? concepts? special abilities?), especially if you explicitly tie it to the PHB. 
However, divine domains are not a uniquely D&D thing. You can probably say that Loki's domain is Trickery and Thor's domain is Thunder without violating copyright, for example. Thus, careful wording might help you dodge your issue. Then again, I'm not a lawyer. 

