(Skt., ‘of the Great Forest’). The longest and perhaps oldest of the principal Upani ads. Composed in prose style between c.8th and 6th cents. BCE, it consists of six chapters attached to the final book of the atapatha Br hma a . The central religious and philosophical themes adumbrated in this Upani ad have been variously interpreted in important commentaries by a kara , R m nuja , and other pivotal religious thinkers of Hinduism.