The quality or state of being easy-going; a relaxed, unhurried, and unconcerned disposition.
From 'easy-going' + '-ness' (abstract noun suffix). This combines two productive English word-building suffixes to create a noun expressing the core quality of the adjective.
Creating 'easygoingness' shows how English speakers playfully extend vocabulary when they need to express an abstract concept—it's technically awkward but perfectly understandable, demonstrating English's flexibility and generativity.
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