Origins
The word 'gnosis' entered English in the early eighteenth century directly from Greek 'gnṓsis' (γνῶσις), meaning 'knowledge,' 'inquiry,' or 'investigation.' The Greek noun derives from 'gignṓskein' (to know, to perceive, to recognize), from the Proto-Indo-European root *ǵneh₃- (to know), one of the most fundamental verb roots in the language family.
The PIE root *ǵneh₃- is remarkable for having produced the primary 'knowledge' vocabulary in virtually every branch of Indo-European. In Greek: 'gnṓsis' (knowledge), 'gnṓmē' (judgment), 'gnṓmōn' (one who knows — the pointer of a sundial), and the verb 'gignṓskein.' In Latin: 'gnōscere/nōscere' (to get to know), 'cognōscere' (to know thoroughly), 'nōtus' (known), 'nōbilis' (well-known, noble), 'nota' (a mark for knowing), 'ignōrāre' (not to know), and 'narrāre' (to make known, to tell). In the Germanic branch: Old English 'cnāwan' (to know), modern 'know,' 'knowledge,' 'acknowledge,' and the Scottish 'ken.' In Sanskrit: 'jñāna' (knowledge), 'jñāta' (known), the root of 'pundit' (from 'paṇḍita,' a learned man).
In English, 'gnosis' is primarily used in the context of Gnosticism, the diverse set of religious movements that flourished in the early centuries of the Common Era. The Gnostics claimed access to a special, direct knowledge of the divine — 'gnosis' — that transcended ordinary faith or intellectual understanding. For the Gnostics, salvation came not through works or belief but through knowledge: specifically, knowledge of one's true spiritual nature and of the nature of the divine realm.
Development
Gnostic thought posited that the material world was created by a flawed or malevolent deity (the Demiurge), and that human souls were sparks of divine light trapped in matter. Gnosis — the direct, experiential knowledge of one's divine origin — was the key to liberation from the material prison. This framework influenced early Christianity, Manichaeism, Mandaeism, and various medieval heresies (Cathars, Bogomils).
The word 'agnostic' was coined in 1869 by Thomas Henry Huxley, Charles Darwin's most prominent defender, from Greek 'a-' (not) + 'gnōstos' (known). Huxley used it to describe his philosophical position that the existence of God was unknowable — neither provable nor disprovable. The word has since broadened to describe uncertainty about any metaphysical claim, and in casual usage it often means simply 'undecided' or 'neutral.'
The term 'Gnostic' (capitalized) refers to the historical religious movements, while 'gnostic' (lowercase) can refer more broadly to anyone claiming direct spiritual knowledge. The adjective 'agnostic' has expanded further, now used in technology ('platform agnostic,' meaning indifferent to which platform is used) and other fields to mean 'without commitment to a particular position.'
Proto-Indo-European Roots
Sanskrit 'jñāna' (knowledge, wisdom) — the same PIE root — occupies a similar position in Hindu and Buddhist philosophy to 'gnosis' in Western esotericism. Jñāna yoga (the yoga of knowledge) is one of the principal paths to liberation in Hindu philosophy, and 'prajñā' (wisdom, higher knowledge) is a central concept in Buddhism. The parallel between Greek gnosis and Sanskrit jñāna illustrates how the same PIE concept of 'knowing' developed into a spiritual category independently in two widely separated branches of the language family.