Thus _brahma upanishad_ is the secret doctrine of _brahma_, and 'whoever follows this _upanishad_' means whoever follows this doctrine.

This seems, however, to be a meaning derived from the nature of the Upanishads themselves, and we are almost inclined to think that the true significance of the word was originally that in which alone occurs, in the early period, the combination _upa-ni-[s.]ad_, and this is purely external: "he makes the common people _upa-ni-s[=a]din," i.e_., 'sitting below' or 'subject,' it is said in _Cat.Br_.ix.

4.
3.

3 (from the literal meaning of 'sitting below').[5] Instead, therefore, of seeing in _upan[=i]sad_, Upanishad, the idea of a session, of pupils sitting down to hear instruction (the prepositions and verb are never used in this sense), it may be that the Upanishads were at first _subsidiary_ works of the ritualistic Br[=a]hmanas contained in the [=A]ranyakas or Forest Books, that is, appendices to the Br[=a]hmana, ostensibly intended for the use of pious forest-hermits (who had passed beyond the need of sacrifice); and this, in point of fact, is just what they were; till their growth resulted in their becoming an independent branch of literature.

The usual explanation of 'Upanishad,' however, is that it represents the instruction given to the pupil 'sitting under' the teacher.
Although at present between two and three hundred Upanishads are known, at least by name, to exist, yet scarcely a dozen appear to be of great antiquity.