There has been an increasing interest in studying the meaning and functions of interjections in recent times following the call of previous scholars for more research on interjections in various languages. This study contributes to this emerging trend as it explores the meaning of an Akan interjection apuu in online discourse and its range of use in different contexts. Data for the study is obtained from social media platforms as well as GhanaWeb. The meaning of apuu is unpacked using the semantic explication technique of the Natural Semantic Metalanguage (NSM) approach. The study demonstrates that instead of merely defining apuu as ‘an interjection that expresses disbelief’, the explication technique describes it in a way that reflects what it actually means to culture insiders and outsiders alike. Also, the explication technique provides the understanding needed to see how apuu is serviceable as a rhetorical device in online discourse among Ghanaians.