The crossword solution for the term 'SPREAD ON THICKLY' is SLAB. SLAB is a noun that refers to a thick, flat piece of material such as stone, concrete, or wood. It is often used in construction and can be used to make walls, floors, and other structures. SLAB is also used to describe a large, flat area of land or a large, flat piece of food such as a cake. In this context, the term 'spread on thickly' could refer to spreading a layer of frosting or icing on a cake or other dessert.