(Egyptian) An aspect of Re (Ra) the solar divinity of the Egyptians, representing the setting sun or the descent of the solar light into the underworld (like Jesus descending into hell).
"[Ra said:] I am the Great Father of the gods and the goddesses. I gave life unto them. I created every living thing that moves upon the dry land and in the sea depths. When I open my eyes there is light: when I close them there is thick darkness. My secret name is known not unto the gods. I am Khepera at dawn, Ra at high noon, and Tum at eventide."
"It is necessary to perform a complete transformation. Let our head and our countenance be from Ra, and our body, our hands, and our legs be from Tum. Ra is the Father. Tum is the body of the Father. Tum is a terribly divine mantra and must never be pronounced in vain or played with, because our Father who is in secret descends immediately from where ever He might be. We must convert ourselves into workers of the Great Work of the Father. Ra is the Christ, is life; Ra is the Second Logos. Tum is the Father, the First Logos. Fire acts and descends when pronouncing TUM. This is a mantra of immense magical sacerdotal power." —Samael Aun Weor, Tarot and Kabbalah