To compliment excessively and often insincerely, especially in order to win favor. To please or gratify the vanity of: "What really flatters a man is that you think him worth flattering\u201d ( George Bernard Shaw). To portray favorably: a photograph that flatters its subject. To show off becomingly or advantageously. To practice flattery. A flat-faced swage or hammer used by blacksmiths. A die plate for flattening metal into strips, as in the manufacture of watch springs.