ǵneh₃-sis-
“act of knowing, knowledge”gnosis, diagnosis, prognosis, agnostic
Abstract from *ǵneh₃- giving Greek gnōsis, English gnosis, diagnosis, prognosis, agnostic.
Discussion
The PIE form *ǵneh₃-sis- (act of knowing, knowledge) is an action noun from the verbal root *ǵneh₃- (to know, to recognise), formed with the process suffix *-sis-. The literal meaning is "the act/process of knowing" — knowledge conceived as an activity, not a static possession.
Greek gnṓsis (γνῶσις, "knowledge, inquiry, investigation") is the direct reflex and the source of a rich English vocabulary: gnosis (spiritual knowledge, especially in Gnostic traditions), gnostic (one who knows, pertaining to knowledge), agnostic (one who does not know — coined by T.H. Huxley in 1869, applying the Greek alpha-privative to gnōsis), diagnosis (knowing through/apart, distinguishing one condition from another), and prognosis (knowing beforehand, predicting an outcome).
The root *ǵneh₃- is one of PIE's most productive bases. Latin (g)nōscere (to know, to come to know) lost its initial g- in the standard form nōscere but preserved it in derivatives: cognōscere (to know thoroughly, whence recognise, cognition, incognito), ignōrāre (to not know, whence ignore, ignorant, ignorance), and nōbilis (knowable, famous, hence noble — a person whose name is known). The English word know itself descends from Old English cnāwan, from PGmc *knēaną, from the same PIE root.
The laryngeal *h₃ in *ǵneh₃- is reconstructed from the o-colouring visible in Greek gnṓ- and Latin (g)nō- (the long ō reflecting *eh₃ > *ō). This laryngeal also explains the ablaut alternation: full grade *ǵneh₃- (know), zero grade *ǵn̥h₃- (which surfaces in Latin gnārus, knowing, and nārrāre, to tell/narrate — literally to make known).
The English word narrate therefore shares its ultimate root with know, recognise, noble, ignore, and diagnosis — a family united by the concept of knowledge and its communication. The narrator is etymologically "one who makes known," the noble person is "one who is known," and to ignore is "to not know."
Sanskrit jānā́ti (he knows) and jñāna- (knowledge) continue the root in the Indo-Iranian branch. The Sanskrit jñāna became a central philosophical term in Hinduism and Buddhism, denoting the highest form of spiritual knowledge — direct experiential understanding as opposed to mere intellectual learning.
Old Irish gnáth (known, customary) and Lithuanian žinóti (to know) confirm the pan-IE distribution. The root's survival in every major branch with the same core meaning makes it one of the most reliable cognate sets in the comparative method — and its derivatives in English alone (know, can, cunning, keen, kenning, narrate, noble, note, notion, notorious, recognise, cognition, diagnosis, prognosis, ignore) demonstrate the extraordinary generative power of a single PIE root.