The word "overbrimming" refers to a condition where something is overflowing with intense emotion or energy. Antonyms of "overbrimming" include underwhelming, dull, lackluster, unimpressive, and uninspiring. Underwhelming denotes a situation where something fails to meet expectations or falls short of being impressive. Dull means boring, uninteresting, and without excitement or enthusiasm. Lackluster suggests that something is lacking in energy, vivacity, or vitality. Unimpressive describes something that is not able to impress, awe or inspire. Finally, uninspiring denotes a lack of creativity or originality, leading to a lack of excitement or interest.