Monstrous is an adjective that describes something gross or shocking. It can refer to the size, shape, or general look of something. If your face or body is monstrous, it's misshapen and horrifying to look at.
The word monstrous describes something that you'd like to avoid looking at, if at all possible. The word comes from the Latin monstruosus, which means "unnatural, deviating from the natural order, hideous." When discussing size, monstrous means that something or someone is so huge it's frightening. Monstrous can also describe someone or something that's extremely cruel or brutal, like a monstrous dictator or monstrous lies.