Two sounds, one family
In present-day English, close is two common words that share a spelling and a history but not a pronunciation. As a verb it usually ends in a voiced sound: close the door, close the shop, close the meeting. As an adjective and adverb it usually ends in a voiceless one: a close friend, stay close, close quarters. The noun follows both. A deal’s close and the close of a speech take the verb’s sound. A cathedral close, the enclosed precinct around a church, takes the adjective’s.
The living core is still physical. Something is made not to pass through, or two things are brought until the gap between them is gone. From that picture English has stretched the word across space, time, feeling, and character: near, finished, intimate, secretive, tight with money.
French on top of an older English verb
The verb is in English by about 1200, already meaning to shut or to cover in. Its immediate source is Old French: the past-participle stem of clore, to shut or cut off. That French verb continues Latin claudere, whose past participle is clausus. In compounds Latin regularly shows a shorter stem, which later English borrowed in include, exclude, conclude, disclose, and enclose.
There was also a native thread. Old English already had clȳsan, to shut, built from clūse, an enclosed place, itself from late Latin clusa, a form of clausa. In early Middle English that verb still appears as clusen. Historical dictionaries treat Middle English closen as a French borrowing that did not land on empty ground: speakers could hear it as a French-shaped pronunciation of the older English verb. Old English beclysan, to shut in, belongs to the same native layer.
The adjective and the spatial noun came by the French route as well. Middle English clos, meaning shut, confined, or secret, is from Old French clos, from Latin clausus. The earliest firm evidence for the adjective is around 1350, in the verse of William of Shoreham. The noun for an enclosed space is a little earlier, from the late thirteenth century. Clause is a doublet of the same Latin participle: another English word from the same past form, not a derivative of close itself.
English already had a native verb for locking and enclosing, lūcan, which survives as lock. Close did not replace it. The two words split the work, one still sounding like a bolt, the other like a door brought to.
A hook before a lock
Latin claudere sits on a reconstructed Indo-European root, written *klau- in some references and *kleh₂w- in others. The reconstructed sense is not an abstract idea of shutting. It is a fastener: a hook, peg, nail, or forked branch used as a bar or bolt in an early building. The same root gives Latin clavis, key, clavus, nail, and claustrum, a bar or barrier, the source of cloister and of claustrophobia. Closet is a later diminutive of the enclosed-space noun: a small shut room.
Cognates keep the hardware in view. Ancient Greek kleís is a bar, bolt, or key, and the related verb means to shut. German schließen, to shut or lock, and Schlüssel, key, belong here, as does Dutch sluiten. Old Church Slavonic ključi is a hook or key; Russian ключ still means key. Old Irish clo is a nail. The Germanic forms begin with s, a known variation at the edge of a reconstructed root rather than a separate invention. Handbooks do not agree on a single spelling of the root, and some scholars gloss it as to close rather than as the hook itself. The disagreement is about reconstruction, not about the Latin and French path into English.
How nearness grew out of shutting
The adjective’s first English senses, in the late fourteenth century, were still about confinement: strictly shut in, pent up, and, by a short step, secret or reserved. A person who is close about private matters is still using that older layer. The dominant modern sense, near, is later, from the late fifteenth century. The route is the verb. To close a gap is to bring two things together, so what has been closed is also what is close. Figurative nearness of people, close friends and close kin, is recorded from the sixteenth century. Attention to small differences, a close reading or close watch, appears in the seventeenth, beside the stingy sense, close with money, as if the hand were kept shut. A close contest, decided by a narrow margin, is a nineteenth-century extension of the same tightness.
The verb moved in parallel. Become shut is late fourteenth century. Bring to an end is about 1400, so a speech can close without any door being involved. Draw near is sixteenth century; military close ranks is mid-seventeenth, later used of any group tightening around itself. Shops that close, and prices quoted at the close, are nineteenth-century trade language. An older sense, to enclose or shut someone in, is now rare in ordinary speech, but it is still visible in close in and in the noun for a walled precinct.
French itself later preferred fermer for the everyday act of shutting a door. English kept close and let it grow a large family of senses that French did not need from clore.
The precinct that still means shut
The origin of the word close is easiest to feel in a cathedral close: not an ending, but a shut space, the same Latin participle that once meant a door was barred. English later split the final consonant to keep the verb and the nearness adjective apart, yet the spelling never followed. Nearby, in this word, is historically a gap that has been closed.