"Celestial Sword - Eatos" is also "Noble Arms" card because it has 「聖剣」 in its Japanese names, but it is unrelated to the other "Noble Arms" cards and the "Noble Knights". In the TCG, it has an archetype condition to clarify this. Additionally, "Celtic Guard of Noble Arms" is a member of the archetype, but it is also unrelated to the other "Noble Arms" cards.
They can only be equipped to Warrior-Type monsters.
If destroyed while face-up on the field and sent to the Graveyard, the player can target 1 face-up Warrior-Type "Noble Knight" monster they control and equip the destroyed card to that target.
In addition, all "Noble Arms" Equip Spell Cards (again, except "Excaliburn" and "Celestial Sword - Eatos") have artworks that depict a sword embedded in stone, a reference to the Arthurian legend of the Sword in the Stone.