In Yogic thinking the first word was OM, the first vibration and sound from which all others emerged. There is no literal translation of OM; its three letters A, U and M signify three periods of time and three states of consciousness and all of existence.
OM (correctly spelt AUM) covers the human threefold experience
A is waking state (representing the physical plane)
U is dream state (representing the mental and astral plane)
M is deep sleep (representing deep sleep state and everything beyond reach of the intellect)
OM has a powerful positive effect upon the nervous system and transforms the physical body setting up new vibrations and awakening dormant physical and mental powers. Because of its universality OM can be used as a mantra by all who are unable to find a teacher.
Paramahansa Yogananda mentions Om/Aum numerous times in his teachings, e.g. on p277 of ‘Autobiography of a Yogi’ ~ “Patanjali speaks of God as the actual Cosmic Sound of Aum that is heard in meditation. Aum is the Creative Word, the whir of the Vibratory Motor, the witness of Divine Presence. Even the beginner in Yoga may soon hear the wondrous sound of Aum.”