The antonyms for the phrase "lack of reserve" are abundant, copiousness, plenitude, abundance, surplus, and profusion. The reserve refers to the inclination of holding back, being cautious or shy in expressing oneself. When someone lacks reserve, they are quite open or even uncontrolled in their interactions or behavior, often resulting in discomfort or awkwardness. On the other hand, abundant, plenitude, or copiousness refer to being bountiful or full of something, indicating an ample or excessive quantity of something. A surplus and profusion, as antonyms for lack of reserve, refer to an abundance, proliferation, or overabundance of something. When individuals exhibit these traits, they are usually confident and comfortable in their expressions, not minding what other people might think or say.