The term 'run smoothly' can be represented by three crossword solutions: HUM (3 letters), PURR (4 letters), and FLOW (4 letters). HUM is a low, continuous sound made by a person or animal, usually indicating contentment. PURR is a low, vibrating sound made by a cat or other animal, usually indicating pleasure or contentment. FLOW is the continuous movement of a liquid or gas in one direction. Together, these three words represent the idea of running smoothly, as if everything is going according to plan with no obstacles or disruptions.