(Sanskrit महत्) Literally, "great." Also, "sacred knowledge, intellect, great principle, power, dominion, lustre, might, greatness."
"Vyasa said, 'Brahma is the effulgent seed from which, existing as it does by itself, hath sprung the whole universe consisting of two kinds of being, viz., the mobile and the immobile. At the dawn of His day, waking up. He creates with the help of Avidya this universe. At first springs up that which is called Mahat. That Mahat is speedily transformed into Mind which is the soul of the Manifest." - Mahabharata
"Bhrigu said, 'There is a Primeval Being, known to the great Rishis, of the name of Manasa. He is without beginning and without end. That Divine Being is incapable of being penetrated by weapons. He is without decay and is Immortal. He is said to be Unmanifest. He is Eternal, Undecaying, and Unchangeable. Through Him are creatures born and through Him they die. He first created a Divine Being known by the name of Mahat. Mahat created Consciousness. That Divine Being created Space." - Mahabharata
"Crude matter is without form. Mahat or the Cosmic Intelligence is its first form." - Swami Sivananda
"In Sankhya philosophy, Mahat is the term used to denote "cosmic mind" or "universal mind." It is the first principle that is derived from Avyakta. It is the first principle that is manifested out of the unmanifested Avyakta. The wheel of the bullock-cart rests on the spokes. The spokes rest on the nave. Even so, the mind rests on Prakriti and Prakriti rests on Brahman. From Mahat comes Ahankara. From Sattvic Ahankara comes mind; from Rajasic Ahankara comes Prana; from Tamasic Ahankara, Tanmatras; from Tanmatras, gross elements; from gross elements, the gross universe. Mind is no other than Ahankara, the idea of 'I'. It is, indeed, difficult to eschew this idea of 'I'. Mind always attaches itself to something objective (Sthula). It cannot stand by itself. It is only this mind that asserts itself as 'I' in this body. The idea of 'I' is the seed of the tree of mind. The sprout which first springs up from this seed of Ahankara is Buddhi. From this sprout, the ramifying branches called Sankalpas have their origin." - Swami Sivananda
"For MAHAT is the first product of Pradhana, or Akasa, and Mahat -- Universal intelligence "whose characteristic property is Buddhi" -- is no other than the Logos, for he is called "Eswara" Brahma, Bhava, etc. (See Linga Purana, sec. lxx. 12 et seq.; and Vayu Purana, but especially the former Purana -- prior, section viii., 67-74). He is, in short, the "Creator" or the divine mind in creative operation, "the cause of all things." He is the "first-born" of whom the Puranas tell us that "Mahat and matter are the inner and outer boundaries of the Universe," or, in our language, the negative and the positive poles of dual nature (abstract and concrete), for the Purana adds: "In this manner -- as were the seven forms (principles) of Prakriti reckoned from Mahat to Earth -- so at the time of pralaya (pratyahara) these seven successively re-enter into each other." - H.P. Blavatsky, The Secret Doctrine
"The seemingly paradoxical use of the sentence "Seventh Eternity," thus dividing the indivisible, is sanctified in esoteric philosophy. The latter divides boundless duration into unconditionally eternal and universal Time and a conditioned one (Khandakala). One is the abstraction or noumenon of infinite time (Kala); the other its phenomenon appearing periodically, as the effect of Mahat (the Universal Intelligence limited by Manvantaric duration). With some schools, Mahat is "the first-born" of Pradhana (undifferentiated substance, or the periodical aspect of Mulaprakriti, the root of Nature), which (Pradhana) is called Maya, the Illusion. In this respect, I believe, esoteric teaching differs from the Vedantin doctrines of both the Adwaita and the Visishtadwaita schools. For it says that, while Mulaprakriti, the noumenon, is self-existing and without any origin -- is, in short, parentless, Anupadaka (as one with Brahmam) -- Prakriti, its phenomenon, is periodical and no better than a phantasm of the former, so Mahat, with the Occultists, the first-born of Gnana (or gnosis) knowledge, wisdom or the Logos -- is a phantasm reflected from the Absolute NIRGUNA (Parabrahm, the one reality, "devoid of attributes and qualities"; see Upanishads); while with some Vedantins Mahat is a manifestation of Prakriti, or Matter." - H.P. Blavatsky, The Secret Doctrine