This essay approaches the vernacular style of Henry Daniel’s Liber uricrisiarum (c. 1379) through his Dominican order’s preoccupation with a properly calibrated preacher’s style. Good preachers must strike a balance to communicate their learning, but never obscurely; to speak plainly but not without grace. Thomas Waleys called this mode a grossus stilus, a simple style, and this is an aptly gross name for Daniel’s way with Middle English, as he instructs his readers in the medieval art of inspecting urine for medical diagnosis. I contextualise Daniel’s own stylistic programme (as articulated in theory in his prologue and then proved in practice in the rest of the Liber) within a long tradition of literary theorising around jargon and plain speech found across the rhetorical manuals and guides to preaching of the Dominican curriculum. While they expressed their arguments in Latin, these texts offered a theory of vernacular eloquence that – as the Liber would prove – could circulate amongst the apparently disparate fields of preaching and Middle English medicine.