musas : mice
The Illunse word for mice (nominative plural) is musas. Musas is a rare last name. In Spanish and Portuguese Musas means Muses, the goddesses who inspire the creation of literature and the arts.
Mice in Latin is muris. Mice in Old English is mýs.
Mouse in Illunse is mus, which is a mix of the Latin word (mus) and Old English word (mús). The Latin and Old English words are basically the same.
By the way, I couldn't find a Quenya or a Sindarin word for mouse.