adjective, noun, verb, idiom, place name · relating to the distant past or antiquity, as opposed to modern times

古往今来，人们对未知世界始终充满着好奇。

proper name · surname Gu

古先生是我们的新老师。

adjective · a prefix used in scientific terminology to refer to prehistoric or geological eras

科学家在岩石中发现了古生物化石。