Taqiyya is an Islamic juridical term whose shifting meaning relates to when a Muslim is allowed, under Sharia law, to lie. A concept whose meaning has varied significantly among Islamic sects, scholars, countries, and political regimes, it nevertheless is one of the key terms used by recent anti-Muslim polemicists such as Robert Spencer or Daniel Pipes, and has been used by US Prosecutors to explain terrorist behavior. This paper seeks to summarize the complex uses of the term and show how a specific concept in a legal system can be used and interpreted by both adherents of that system and enemies in a wide variety of ways, taking on different meanings while referring to effectively the same set of practices. The term is debated in a scholarly way in the scholarly literature, as an ethnographic term, and finally, as an operational concept used as a tactic in a war and demanding countertactics tailored to it. The paper will discuss the social purpose of having such ambiguous concepts available within one's society, and the idea that making the ambiguous specific can be a valuable weapon in polemical attack.