plan·et·ol·o·gy \ˌplanəˈtäləjē\noun (-es-s) Etymology:planet + -ology (as in cosmology) : a science that deals with the condensed matter (as the planets and natural satellites) of the solar system • plan·et·o·log·i·cal\-_təlˈäjə̇kəl \adjective • plan·et·ol·o·gist\-ˈtäləjə̇st \noun