>>40375
https://en.wikipedia.org/wiki/Brahmastra
The Brahmastra is described as a weapon that creates a fireball capable of destroying the world, and is intended to be used as a last resort, never for combat. The after-effects sound exactly how an ancient civilization would describe a massive high-temperature explosion, but not quite a nuke. More like a MOAB.
The Brahmashirsha Astra is an even more powerful weapon. It is said to be capable of destroying gods, and can be invoked from any object, even grass. The weapon manifests the heads of Brahma and then causes what is essentially an ancient civilization's description of a nuke, with fallout that renders an area uninhabitable for twelve years.
The Brahmanda Astra is said to destroy the universe. Since they didn't have knowledge of space travel, this could either just be a planet killer that takes the Hindu mythological realms with it or an actual universe killer.