any of a class of speculative prose treatises composed between the 8th and 6th centuries b.c. and first written a.d. c1300: they represent a philosophical development beyond the Vedas, having as their principal message the unity of Brahman and Atman.
Origin: < Sanskritupaniṣad, equivalent to upa near + ni- down + -ṣad, sandhi variant of sad-sit1
Hinduism any of a class of the Sanskrit sacred books probably composed between 400 and 200 bc and embodying the mystical and esoteric doctrines of ancient Hindu philosophy
[C19: from Sanskrit upanisad a sitting down near something, from upa near to + ni down + sīdati he sits]
class of treatises in Skt. literature, 1805, from Skt. upa-nishad, lit. "a sitting down beside," from upa "near to" (see up) + ni-shad "to sit or lie down."