Thermoplastic assemblies, methods of defining thermoplastic assemblies, aircraft that include the thermoplastic assemblies, and aircraft that are formed utilizing the methods are disclosed herein. The methods include heating a joining structure and pressing a thermoplastic layer against a base of the joining structure. The pressing includes transferring thermal energy from the joining structure to the thermoplastic layer and penetrating the thermoplastic layer with a plurality of reinforcing projections of the joining structure. The pressing also includes adhering the thermoplastic layer to a surface of the base and to a surface of the plurality of reinforcing projections. The thermoplastic assemblies include the thermoplastic layer and the joining structure.