The flagship of Queen Paolana of Hysperia, a spacefaring vessel dressed up in Renaissance-fair style, which the Cerritos was sent to repair in 2381.
The Monaveen is the royal ship of Hysperia, a human colony whose people live out a medieval fantasy and describe their technology in the language of magic. Its warp core is known as the dragonsbreath engine. It appears in the Lower Decks episode Where Pleasant Fountains Lie.
Queen Paolana is the mother of Andy Billups, chief engineer of the Cerritos, who gave up his claim to the throne to join Starfleet. She asks for his ship by name when the Monaveen breaks down.
The breakdown is a plot. Paolana stages an explosion and her own death, along with Rutherford's, so that Billups will feel bound to take the crown, which by Hysperian custom means first losing his virginity. Rutherford turns up alive just in time.