Definition of insecure. 1  1 : not confident or sure : uncertain feeling somewhat insecure of his reception. 2  2 : not adequately guarded or sustained : unsafe an insecure investment. 3  3 : not firmly fastened or fixed : shaky the hinge is loose and insecure.
For men, semi-formal attire means wearing a full suit, with vest optional. A tie, either bow or straight, should be worn, and the shirt should be a simple button down. Suit fabric choices are primarily wool gabardine or cashmere. However, a wool blend will do.
For a formal wedding a tuxedo is ideal though in today's day and age a dark suit is also acceptable. Essentially choose whichever garment you already own, and if you own neither rent a tuxedo. For more information, you may also want to read our guide to black tie attire. If the wedding is semi formal then you should either wear a suit or a sport coat. There is no real ideal here, and either is appropriate; so choose whichever garment you are more comfortable in and looks the best. For more information, you may want to read our guide on Semi-Formal Attire.