Origins
The word 'cognition' refers to the mental processes involved in gaining knowledge and comprehension, including thinking, knowing, remembering, judging, and problem-solving. It entered English in the fifteenth century from Latin 'cognitiōnem,' the accusative of 'cognitiō,' meaning 'a getting to know, acquaintance, knowledge, recognition.' The Latin noun derives from the past participle stem 'cognit-' of the verb 'cognōscere,' meaning 'to get to know, to recognize, to investigate.'
The verb 'cognōscere' is itself a compound: 'co-' (an intensifying prefix, from 'cum,' meaning 'together' or 'thoroughly') plus 'gnōscere,' an archaic form of 'nōscere' (to come to know, to learn). The initial 'g' in 'gnōscere' was lost in classical Latin 'nōscere' but preserved in the compound 'cognōscere,' where the preceding prefix protected it. This archaic 'g' is the telltale marker connecting the word to its PIE ancestor.
That ancestor is the root *ǵneh₃-, one of the most securely reconstructed and widely distributed roots in Proto-Indo-European. Its basic meaning was 'to know,' and it proliferated across every major branch of the Indo-European family. In the Germanic branch, it produced Old English 'cnāwan' (to know, to perceive), which became Modern English 'know.' The initial 'kn-' cluster, still preserved in spelling, was pronounced in Old and Middle English — 'know' was once 'k-now' — before the 'k' fell silent in Early Modern English.
Latin Roots
In Greek, *ǵneh₃- produced 'gignōskein' (to know, to perceive), which generated 'gnōsis' (knowledge), 'gnōmē' (judgment, opinion), and 'gnōmōn' (one who knows, an indicator — the part of a sundial that casts the shadow). English borrowed extensively from this Greek family: 'diagnosis' (knowing through examination), 'prognosis' (knowing beforehand), 'agnostic' (not knowing), and 'gnostic' (relating to knowledge, especially spiritual knowledge).
In Sanskrit, the same root produced 'jñā-' (to know), yielding 'jñāna' (knowledge) — a central concept in Hindu and Buddhist philosophy, referring to the highest form of spiritual understanding. The 'jñ-' cluster in Sanskrit is the regular reflex of PIE *ǵn-, demonstrating the systematic sound correspondences that allow linguists to reconstruct the proto-language.
The Latin branch was spectacularly productive. From 'cognōscere' and 'nōscere,' English acquired: 'recognize' (to know again), 'cognizant' (aware, knowing), 'incognito' (unknown, in disguise), 'connoisseur' (one who knows, an expert judge — borrowed through French), 'noble' (from Latin 'nōbilis,' originally 'gnōbilis,' meaning 'knowable, famous'), 'note' (from 'nota,' a mark by which something is known), 'notion' (an idea, something known), 'notorious' (known widely, usually for something bad), and 'annotate' (to mark with notes).
Scientific Usage
The word 'cognition' itself remained a relatively technical, philosophical term for centuries after its introduction to English. Scholastic philosophers used it in discussions of how the mind apprehends reality. It gained broader currency in the nineteenth century as psychology emerged as a scientific discipline, and it became a central organizing concept in the twentieth century with the rise of cognitive science — the interdisciplinary study of mind and intelligence that unites psychology, neuroscience, linguistics, philosophy, and computer science.
The adjective 'cognitive' (relating to cognition) dates from the 1580s but became truly ubiquitous only in the mid-twentieth century. 'Cognitive dissonance,' coined by psychologist Leon Festinger in 1957, entered popular vocabulary as a description of the discomfort felt when holding contradictory beliefs. 'Cognitive behavioral therapy' (CBT), developed in the 1960s, became one of the most widely practiced forms of psychotherapy. Today, 'cognitive' appears in compounds spanning science and technology: cognitive load, cognitive bias, cognitive computing, cognitive decline.
The journey from PIE *ǵneh₃- to modern 'cognition' illustrates how a single root meaning 'to know' could generate vocabulary for the entire spectrum of human knowledge — from the everyday ('know'), to the philosophical ('gnostic'), to the scientific ('cognitive'), to the culinary ('connoisseur'), to the dramatic ('incognito') — across five millennia and dozens of languages.