The British spelling of the process of making something circular in shape or form, or distributing information to many people through a circular letter.
From 'circularise' (British spelling) plus the suffix '-tion', which comes from Latin and indicates the result or process of an action. This is the British variant of 'circularization.'
The British and American split on this word (circularisation vs. circularization) is like a living fossil of spelling wars from the 1800s, when reformers wanted to simplify English but different countries went different directions.
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