IPA: /ˈkæʒ.ʊ.əl.nəs/
KK: /ˈkæʒuəlnəs/
A state or quality of being relaxed and informal, without strictness or formality.
Her casualness made everyone feel comfortable at the party.
Casualness → It is formed from "casual" (from Latin *casualis*, meaning happening by chance) and the suffix "-ness" (meaning the state or quality of). The word "casualness" refers to the state of being informal or relaxed, often occurring by chance rather than by design.
Think of 'happening by chance' ('casual') to remember that 'casualness' means the quality of being informal or relaxed.