Collaborative tagging systems have emerged in recent years to become popular tools for organising information on the Web. While collaborative tagging offers many advantages, they also suffer from several limitations, with a major one being the existence of ambiguous tags. To understand what an ambiguous tag is intended to mean, we need to know the contexts in which it is used. Instead of using common large scale clustering techniques on folksonomies, we believe tags can be better contextualised by the social contexts in which they are used. We propose a method to reveal semantics of ambiguous tags by studying the collective user behaviour in a tagging system. In this paper we describe our proposal and some results of our preliminary experiments. We also discuss the significance of the work and how it can be evaluated.