A principal support or most important fundamental element; the chief foundation or strongest supporter of something.
From 'arch-' (chief, principal) plus 'pillar' (from Latin 'pilare,' related to 'pila' meaning stake or column). The word suggests supreme structural or metaphorical support.
The 'five pillars of Islam' are important, but if you heard about the 'archpillar,' that would be the one pillar so fundamental that the entire religion rests on it!
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