Kena Upanishad
The word Upanishad (upa-ni-shad) consists of, "Upa" means "near;" "ni" means "down;" "shad" means "to sit." Thus, Upanishad is to sit down near the teacher to discuss, learn, practice, and experience. There are some 200 or more Upanishads. Some are lost and are only known about because of being referenced in other Upanishads.
Most of the Upanishads were kept secret for centuries, only passed on to others orally in the form of Shloka (a category of verse line developed from the Vedic Anustubh meter).
Kena (Sanskrit: केन) literally means, depending on the object-subject context, "by what, by whom, whence, how, why, from what cause". This root of Kena, in the sense of "by whom...