Dualcast

X-Magic is a recurring ability which allows a character to cast two spells in one turn.

Final Fantasy V
X-Magic was a Level 4 ability of the Red Mage Class

Final Fantasy VI
If a character equipped the Gem Box Relic, he or she could cast two spells in one turn.

Final Fantasy VII
The W-Magic Materia allows a character to cast two spells in one turn.

Final Fantasy IX
When Vivi Ornitier Trances, he can cast two Black Magic spells in one turn. When Eiko Carol Trances, she can cast two White Magic spells in one turn.

Final Fantasy X
This ability is renamed Doublecast in this game, and it only allows a character to cast two Black Magic spells in a row. It is located in Lulu's section of the Sphere Grid, but several locks must be passed first.