'Occlude' means 'to close against' — not merely shutting, but shutting in opposition to something passing.
Definition
To block or close up a passage or opening; in dentistry, to bring the upper and lower teeth into contact; in meteorology, to cut off a warm air mass from the surface by forcing it aloft.
The Full Story
Latin16th centurywell-attested
From Latin 'occlūdere' (to shut up, to close off), a compound of 'ob-' (against, in theway of) and 'claudere' (to shut, to close). Latin 'claudere' derives from PIE *kleh₂w- (a hook, a peg; to close with a hook or bar), which also produced Greek κλείς (kleís, key, bolt), κλείω (kleíō, I close), Old Irish 'cló' (nail), and Lithuanian 'kliūti' (to get caught, to snag). The PIE image is concrete: a door secured by a hooked bar. From 'claudere' English
Did you know?
In meteorology, an 'occluded front' forms when a cold front overtakes a warm front and lifts the warm air entirely off the ground — literally shutting it away from the surface. The weather term perfectly preserves the Latin sense: the warm air is 'closed against' and blocked from reaching the earth.
front, shutting it off from the surface), and chemistry (a solid occluding gas by trapping it within its structure). Each technical sense preserves the original PIE metaphor of barring shut, extended from wooden doors to atmospheric boundaries and molecular lattices. Key roots: claudere (Latin: "to shut, to close"), ob- (Latin: "against, in the way of"), *klāu- (Proto-Indo-European: "hook, peg, crooked branch (used for fastening)").