Thornbush is a unique term used to describe a prickly shrub that can cause physical harm to those who come into contact with it. As such, there are a few synonyms that can be used interchangeably to give a similar meaning and context. Some of these synonyms include bramble, briar, thicket, and underbrush. All these words can be used to describe vegetation that has thorns or prickly leaves and can be difficult to navigate through. Other synonyms for thornbush may include burr, prickle, or spike. These words help to paint an accurate picture of the sharpness and potential danger that comes with encountering this type of plant.