The term 'Knob on a Shield' can be summarized by two crossword solutions: UMBO (4 letters) and BOSS (4 letters). UMBO is an architectural element found in Gothic architecture, which is a pointed arch or vault that projects beyond the main wall. It is usually decorated with a shield or coat of arms and often has a knob or finial at the top. BOSS is a term used to describe a leader or supervisor, usually in a workplace setting. In this context, it could refer to the person responsible for the design and construction of the shield.