A broad smile is a powerful expression that can convey a range of emotions from happiness to pure joy. When searching for synonyms, you might consider words like grin, beam, or flash. Grinning implies a mischievous or cheeky nature, while beaming suggests a warm and radiant smile. A flash of the teeth might imply a brief, momentary expression of delight. Other synonyms could include a wide smile, a big smile, a sunny grin, or a ear-to-ear smile. Ultimately, the perfect synonym will depend on the context in which the smile occurs, the personality of the individual, and the emotions being conveyed.