moonbat /ˈmuːnˌbæt/adjective 1noun 1forms 3 adjective1 •(informal, disapproving) (of ideas) Absurd or obviously untruthful. noun1 •(informal, offensive) A liberal (someone with a left-wing ideology).So, what do moonbat professors do when they're not attacking military recruiters, the Bush administration, cameramen, and College Republicans? — 2005 formsmoonbats · more moonbat · most moonbat