Traditional lexicographical evidence for the study of multilingualism in medieval England has relied largely—if not exclusively—on vernacular sources, either in Middle English or Anglo-Norman. Meanwhile, only historians and very few philologists have taken advantage of the extensive collections of administrative documents written in Medieval Latin and preserved in archives all around the country. This under-researched documentary material uniquely reveals the complexities of the medieval multilingual world: the synergy between Medieval Latin, Anglo-Norman, and Middle English best materialises on the lexical level of these texts, where a large multilingual repertoire is pragmatically put into action. In this article, I concentrate on one of such unexplored documentary sources, The Inventories and Account Rolls of the Benedictine House or Cell of Jarrow in the County of Durham (1303–1537), and I survey four of the semantic fields representing its basic concerns: materials, tools, animals, and household goods. I discuss the intricate ways in which lexical material from Medieval Latin and the vernaculars converges in these inventories and accounts, and how often contemporary taxonomical efforts are unavailing.