Ar tonelico (アルトネリコ, Arutoneriko?) is the name given to the Symphonic Power amplifier that was designed and developed in the region of Sol Ciel, and also to all of its related mechanisms and facilities. This means that the Tower of Frelia and the Tower of Harvestasha also receive this name.
The name itself means The Only Divine Tree in Hymmnos, and etymologically speaking, it comes from the Japanese word トネリコ (toneriko) which translates directly to "Ash Tree". This was meant to imply that each Tower has a role similar to a World Tree/Tree of Life in the myths of many cultures of Earth, which is appropriate, given that they became the sole havens where life could prosper after the Grathnode Inferia catastrophe.