Bonny means pretty in a healthy, bright way — a bonny baby has colour in the face and looks well cared for; a bonny lass is a good-looking girl, said with warmth, not with fashion-magazine chill. It is especially Scottish and northern English. Further south, and in most classrooms, people just say pretty, lovely, or good-looking. You still hear it in songs, in stories set in Scotland, and from grandparents. It is kind, not snarky. There is also the spelling bonnie, same word, often in names (Bonnie) and in 'bonnie Scotland'. It is not bony (thin, showing bones), and it is not a fancy Latin bonus. Older and younger speakers: older Scottish speakers use it naturally; many young learners only meet it in songs. People stretch it a little — 'a bonny wee boat' — to mean pleasing, not only a person's face.