Peer-to-peer (P2P) computing has become a popular distributed computing paradigm thanks to abundant computing power of modern desktop workstations and widely available network connectivity via the Internet. Although P2P file sharing provides a scalable alternative to conventional server-based approaches, providing efficient file search in a large scale dynamic P2P system remains a challenging problem. In this paper, we propose a set of mechanisms to provide a scalable keyword-based file search in distributed hash table (DHT)-based P2P systems. In particular, we address the problem induced by common keywords that are associated with a large number of files and thus require excessive storage consumptions from the hosting peers. Our proposed architecture, called keyword fusion, adaptively unburdens the peers overloaded with excessive storage consumptions due to common keywords and reduces network bandwidth consumption by transforming users' queries to contain more focused search terms. Through trace-driven simulations, we show that keyword fusion can reduces the storage consumption of the top 5% most loaded nodes by 50% and decrease the search traffic by up to 68% even in the modest scenarios of combining two keywords.