While anything that has the shape of a bulb — like an onion or a light bulb — can be described as bulbous, it almost always describes someone's nose. It's not very nice to tell your friend he has a bulbous nose, though it may be accurate. You can also call a plant bulbous if it's grown from a bulb. This is the earliest, 16th century use of the word, while the "bulb-shaped" meaning came along about 200 years later.