The word Upanishad (Upaniṣad ) is derived from the Sanskrit verb “sad”, preceded by the preverbs upa- and ni-.
The most common meaning of sad is “to sit.” The preverb upa- may express proximity (“near”), and the preverb ni- a downward motion.
Upanishad may therefore be translated as “sitting down near” someone. The term is traditionally interpreted as a reference to the student sitting down at the teacher’s feet to receive the secret teachings about ātman and brahman.
The Upanishads themselves often refer to teachers and students and the process of learning; in fact, the student–teacher relationship is the primary social relationship in the Upanishadic texts, far more significant than the relationships between parents and children or between husband and wife.
Finding the right teacher is crucial, as the wisdom seekers in the Upanishads discover. The seekers in the Upanishadic texts end up finding the knowledge they need both in learned Brahman priests and in more unlikely preceptors such as kings, or even talking animals.
The teacher’s background matters far less than the knowledge he (or she or it) possesses. It is perhaps reasonable, then, that the texts themselves are named after the act of sitting down at the feet of a teacher to absorb the essential ideas about ātman and brahman.