trilithonPronunciation: /trʌɪˈlɪθ(ə)n/ (also trilith /ˈtrʌɪlɪθ/)Definition of trilithon noun Archaeology a megalithic structure consisting of two upright stones and a third across the top as a lintel. Origin: mid 18th century: from Greek, from tri- 'three' + lithos 'stone'