American spelling: the process of making something circular in shape or form, or distributing information through circular notices to many people.
From 'circularize' (American spelling) plus '-ation,' a suffix from Latin indicating a process or result. This is the American variant of 'circularisation,' standardized in the 1800s.
The Great Spelling Divide of English—why Americans chose '-ize' and British chose '-ise'—traces back to dictionary makers like Noah Webster who wanted to 'fix' English and make it more 'logical' using Latin rules.
Complete word intelligence in one call. Free tier — 50 lookups/day.