The word "un-gainliness" refers to the lack of grace or awkwardness in movement, appearance, or behavior. Its antonyms would be words that describe elegance, finesse, and poise. Some possible antonyms for "un-gainliness" are gracefulness, fluidity, nimbleness, agility, smoothness, dexterity, lightness, finesse, deftness, and litheness. These words connote a sense of ease and beauty in motion, as well as a certain degree of control and precision. By using these antonyms in context, one can paint a picture of graceful and effortless movements, whether in dance, sports, or everyday life.