"made shut, not open," c. 1200, past-participle adjective from close (v.). Closed circuit "complete, unbroken (electrical) circuit" is attested from 1827; closed shop"workplace in which only union members are employed" is from 1904; closed system first recorded 1896 in William James as "complete and unalterable system (of doctrines, etc.)." Later used in a physical sense, "system in which the total mass or energy remains constant."
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