The word 'cloister' opens a door — or rather, closes one — onto one of the most productive root families in the English language. From Latin 'claudere' (to close, to shut), through 'claustrum' (a lock, a bolt, an enclosed place), the word carries the fundamental concept of enclosure that defines monastic architecture and monastic life.
'Cloister' entered English in the thirteenth century from Old French 'cloistre,' itself from Latin 'claustrum.' In its architectural sense, a cloister is the covered walkway that typically surrounds a quadrangular courtyard in a monastery, convent, or cathedral. One side is a solid wall (often the wall of the church or chapter house), while the other is open to the courtyard through a colonnade of arches. The cloister served as a circulation space, a place for contemplative walking
In its extended sense, 'cloister' means religious seclusion itself — to be 'cloistered' is to be shut away from the world. Cloistered religious orders (such as the Carmelites and the Poor Clares) practice strict enclosure, rarely leaving their monastery or convent. The verb 'to cloister' means to seclude or shut away, and it has passed into general English use for any form of sheltered isolation: one can be 'cloistered' in an ivory tower, in academia, or in privilege.
The Latin root 'claudere' is spectacularly productive in English. 'Close' (to shut — the most direct descendant) came through Old French 'clos.' 'Closet' (a small enclosed room) is a diminutive. 'Clause' (a section of a legal document or a sentence) comes
'Recluse' (from re- + claudere, to close away) describes a person who has shut themselves away from society — essentially the secular equivalent of a cloistered monk. 'Claustrophobia' (fear of enclosed spaces) combines 'claustrum' with Greek 'phobos' (fear) — a hybrid formation typical of modern scientific vocabulary.
German 'Kloster,' meaning monastery, comes from the same Latin 'claustrum.' This means that the German word for a monastery and the English word for a covered walkway are etymologically the same word, having diverged in meaning as they were borrowed into different languages at different times. German took the word to mean the enclosed institution as a whole; English (following French) narrowed it to the enclosed architectural space within the institution.
The architectural cloister reached its highest development in medieval European monasteries, particularly those built under the Benedictine, Cistercian, and Dominican rules. The quadrangular layout — church on the north, chapter house and dormitory on the east, refectory on the south, cellarium on the west, with the cloister walk connecting them all — became standard across Europe from the ninth century onward. The cloister was the circulatory system of the monastery, and its name — 'the enclosed space' — was the architectural expression of the monastic vow to separate from the world.