I'm indecisive as to what title to chose for a novel I finished writing. I went for a pseudo-Latin title : "Apex Fantasia" as it is a fantasy novel. But I still wonder if I can find alternatives that sound more right, and I'm not sure of the meaning of "Fantasia" or even if it is a real classical Latin word to begin with.
Fantasia is Italian, not Latin, though you happen to be in luck, for the Latin is spelled phantasia, and it has two distinct meanings:
I.an idea, notion, fancy (post-Aug.): “Nicetas longe disertius hanc phantasiam movit,” Sen. Suas. 2, 15: “cor tuum phantasias patitur,” Vulg. Ecclus. 34, 6.—As a term of reproach: phantasia, non homo, a mere notion or fancy, the mere semblance of a man, Petr. 38 fin. (in Cic. Ac. 1, 11, 40; 2, 6, 8 al., written as Greek, and translated visum).—
II. A phantom, apparition: “(animus) colligit visa nocturna, quas phantasias nos adpellamus,” Amm. 14, 11, 18.
Unlike in English, apex is not an adjective (apex predator, for example, is non-sense in Latin). I don't know what you're trying to say with that title, but it's not grammatical as it stands. Other potential options include summus, primus, or optimus, depending on what nuances you're trying to get across.