The objective is to identify the outlier. (1) Mustard is an oilseed, providing seeds for oil extraction. (2) Rapeseed (Canola) is an oilseed, also used for oil. (3) Groundnut (Peanut), though botanically a legume, functions as a nut and is an oilseed. (4) Cashew nut is a tree nut, primarily consumed as a nut; oil extraction is secondary. Mustard, Rapeseed, and Groundnut are primary edible oil sources (oilseeds). Cashew nut is primarily a tree nut. Therefore, Cashew nut is the dissimilar item.