Which is the proper term to use in the Warhammer Fantasy universe: Ork? Orc? Orcish or Orkish?
jh
Is it Orcish or Orkish?
Orc = WF, Ork = Wh40k
I'm pretty certain the orcs don't care! 
"Orc" is Albion (english)
"Ork" is Reikspiel (deutsch)
That's how I see and use it.
As the first answer said, "Orc" is what they're called in Warhammer. While in Warhammer 40k they're called "Ork".