From Latin 'claudere' (to shut) — the unprefixed heir of a verb that built 'include,' 'exclude,' 'conclude,' and 'clause.'
To shut or cause to shut; to bring to an end; near in space, time, or relationship; a narrow passage or courtyard, especially one leading to a cathedral.
From Old French 'clos' (closed, shut, past participle) and 'clore' (to close, to shut), from Latin 'claudere' (to shut, to close) via its alternative form 'clōdere' and past participle 'clausus/clōsus.' The PIE root is *klāu- (hook, peg). This is the direct English descendant of 'claudere' — the same root that, through prefixed Latin compounds, produced 'include,' 'exclude,' 'conclude,' 'preclude,' 'seclude,' and 'occlude.' English 'close' is the family patriarch in disguise. Key
English 'close,' German 'Schloss' (lock, castle), and Latin 'claudere' all descend from the same PIE root *klāu- (hook or peg for fastening). A German 'Schloss' is both a lock and a castle — a castle being, at its core, a place that is locked and closed against enemies. The words have diverged so far in sound