Stopped from growing as big or as fully as it should have. A stunted tree stayed small because it had no light; a plant is stunted by poor soil; in serious writing, children who do not get enough food may be stunted in their growth — this is a real medical term, used by doctors and aid agencies, so handle it with care when talking about people. English also uses it for things that are not alive: stunted growth in an economy, a stunted career, a stunted friendship, someone's stunted emotional development. In every case the important idea is not simply 'small' — it is 'smaller than it was meant to be, because something got in the way'. That sense of interrupted potential is the whole word. It leans formal to neutral, and it almost always implies a cause, even when the cause is not named.