Deals damage to all undead foes.Final Fantasy description
Despite the similar name in English releases, the spell is not the same as the Diaga (ディアガ, Diaga?) ability that originated in Final Fantasy XI, which often deals light-elemental damage to enemies within an area of effect.
Diaga (HRM3 on the NES and Dia3 in Final Fantasy Origins) is a level 5 White Magic spell, which inflicts a large amount of damage against all undead enemies and has no effect on other types of enemies. In the NES and Origins releases, it inflicts between 80 and 240 damage, while in subsequent releases it inflicts damage depending on the caster's Intelligence.
Dia means "day" in Portuguese, Spanish and Occitan.
In ancient Greek religion and folklore, Dia means "heavenly", "divine", or "she who belongs to Zeus". The name is attributed to several figures and treated like an honorific or title.