Entry 1 sense Webster, 1913 Tranquillity /trăng-kwĭl'-ĭt-ē/ · Tran·quil·li·ty · IPA /tɹæŋˈkwɪl.ɪ.ti/ 01 n. The quality or state of being tranquil; calmness; composure. 1. The quality or state of being tranquil; calmness; composure.