This is a hard haiku constraint because ETUDE is culturally loaded and somewhat formal. It pulls toward art-language and abstraction, while haiku usually wants immediacy, image, and felt motion. The stronger poems solve that by giving the word a real field to live in before it arrives. Starr’s “IRATE barn swallows / Dive and eat THOSE mosquitoes / ETUDE of dusk swarm” is a good example: the poem first builds a vivid natural pattern, then uses ETUDE to name that pattern as study and repetition. Across the set, the better entries treat the target word not as ornament but as a way of framing practice, discipline, or recurring motion, which is what keeps a refined word like this from feeling pasted onto the haiku.