astronomical UK /ˌæs.tɹəˈnɒm.ɪ.kəl/US /ˌæs.tɹəˈnɑm.ɪ.kəl/ adjective2 •Of or relating to astronomy.Finally, all men saw that astronomical knowledge lied not, and they awaited the comet. — 1839 •Very large; of vast measure.At the moment he wondered why anyone would want to visit Khatka, let alone pay some astronomical sum for the privilege. — 1959 formsmore astronomical · most astronomical