An unwanted plant is a plant that is not wanted in a particular area or environment. The term can be broken down into two crossword solutions: SPY (3 letters) and WEED (4 letters). SPY stands for 'Substances Prohibited from Yielding, ' which is a term used to describe plants that are considered invasive and are not native to the area. WEED stands for 'Wildly Evasive Exotic Destructive, ' which is a term used to describe plants that are considered to be a nuisance and can cause damage to the environment.