Present participle of 'circularize': the act of making circular or distributing information to many people (American spelling).
From 'circularize' plus '-ing,' the gerund and present participle suffix from Old English. The '-ing' is one of English's most versatile affixes.
The '-ing' suffix is so powerful that it's created a whole class of words that can work as nouns, adjectives, or verbs—'circulating' can mean a person who circulates, the act of circulating, or something that is currently circulating.
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