This paper explores functions of pseudonyms in written threatening communication from a cognitive sociolinguistic perspective. It addresses the semantic domains present in pseudonyms in a corpus of 19th-century Irish English threatening notices and their cognitive functions in the construction of both cultural-contextualised threat and the threatener’s identity. We identify eight semantic domains that are accessed recurrently in order to create threat. Contributing to the notion of threat involves menacing war, violence, darkness and perdition directly, while also constructing a certain persona for the threatener that highlights their motivation, moral superiority, historical, local and circumstantial expertise, and their physical and mental aptitude. We argue that pseudonyms contribute to the deontic force of the threat by accessing cultural categories and schemas as well as conceptual metaphors and metonymies. Finally, we suggest that pseudonyms function as post-positioned semantic frame setters, providing a cognitive lens through which the entire threatening notice must be interpreted.