The number of Internet-connected everyday objects grows thanks to the Internet of Things (IoT). The trend with this new paradigm where smart embedded devices, people, and systems are connected, is that over the next few years we could see a shift in the notion of what it means to be 'on the Internet'. In this context, Wireless Sensor Network (WSN) technology is an essential component of IoT because it consists of a collection of sensor nodes connected through wireless channels, capable of providing digital interfaces to the real-world things. Moreover, as it occurs in IoT, specific WSN applications can be applied to a wide variety of domains like health, agriculture, logistics, wearable computing and others. However, recent works considered as WSN applications are being called as IoT applications without distinguishing the new features that characterize this denomination. Hence, in this paper we propose to contrast IoT and WSN from a conceptual overview, aiming to find out the relationship between them and to highlight their differences in terms of (i) the thesaurus proposed by IEEE, ACM and UNESCO, (ii) by performing a chronological review of the concepts since these terms appeared, (iii) the definition issued by reference organizations and researchers, and (iv) the main application requirements addressed by reference architectures proposed for both fields of study.