A dominant narrative, produced and reproduced especially by terrorism scholars, holds that terrorism in its worst form is religious. The most dangerous and non-negotiable form of terrorism, in other words, is the religious kind. At the same time, there is a recurring implication, proposed by many terrorism scholars and reflected in public discourse, that terrorism, no matter its official designation, is always inherently ‘religious’ or ‘religious-like’. Both this implication and the dominant narrative about the uniquely dangerous character of ‘religious terrorism’ – which I summarise as the Religious Terrorism Thesis – builds on colonial knowledge and assumptions about ‘religion’. Religion is also, as I argue, written into the category ‘terrorism’ and enables its negative discursive power and the colonial imagination of ‘terrorism’ as racialised and a system-threat to (Western) modernity. Terrorism, therefore, can never constitute a neutral signifier of a specific kind of political violence. Instead, it functions as a negative ideograph to Western societies, which means it functions to uphold the project of Western modernity/coloniality. The Religious Terrorism Thesis, which I identify as the foundation for the dominant discourse on terrorism today, is a crucial element of coloniality and justifies many controversial and contemporary counterterrorism practices.