Entry 1 sense Webster, 1913 Triassic /trīˌ-ăs'-ĭkˌ/ · Tri·as·sic · IPA /tɹaɪˈæs.ɪk/ 01 a. Of the age of, or pertaining to, the Trias. 1. Of the age of, or pertaining to, the Trias.(Geol.)