I think that if you wanted you could simply make something up and explain it as having the properties of magic. As long as you explain the meaning of the word you could use any.
Poop. Example; "I want to be trained in poop." "I don't know what kind of poop I have." "I am a skilled poop"/"I am quite skilled with poop." "They were juggling balls of poop with ease." "Don't use your poop here." "Her overuse of poop weakened her." You're welcome.
I would go with anima given it is more specific than art. Though the dark arts or a different adjective could make art more specific to your story.
You could always try making up a word, or using other magic-sequel words as a basis. "Arcana" comes to mind. Something like that at least.
"Anima" feels more primal, though dictionary.com says it's "soul; life" and "the inner personality that is turned toward the unconscious of the individual", so it could work for you. "Art" or "the Art" sounds more high-fantasy, D&D-ish. "Mana" could work, or "sorcery" (though that generally has a darker connotation). In my WIP, mages are called (elemental) Wielders (they manipulate, or Wield, elemental energy). Maybe if you figure out what magic-users are called, you could reverse-engineer a name for magic. You could also go with specific names for each type - in Game of Thrones, for instance, Melisandre is a Shadowbinder. In WoT, they're called Channelers (generic term for both male/female mages), who channeled the (One) Power (or the True Power, in Ishamael's case). Edit: There's also an "energy type" generator on Fantasy Name Generators.