theoretical UK /ˌθɪəˈɹɛtɪkəl/US /ˌθi.əˈɹɛt.ɪ.kəl/ adjective1 •Of or relating to theory; abstract; not empirical.We may look upon this figure as representing in section a theoretical wing-form, or aerofoil — 1907 formsmore theoretical · most theoretical