Plural of circulation; instances of moving around or through a system; the flow of blood, air, or other substances through passages.
From 'circulate' + '-tion' (state or action) + plural '-s.' Medieval Latin 'circulatio' meant 'a moving in a circle.'
There's blood circulation, air circulation in buildings, circulation of ideas through libraries (circulation desks!), and even atmospheric circulation—circulation connects all these systems through one motion!
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