Harbingering means to announce or signal the arrival of something. The antonyms of this word would be to hide, conceal, or suppress the announcement or signal of something's arrival. In a positive sense, we could use antonyms like downplaying, underestimating, or understating the importance of something, while in a negative sense, we could use antonyms like cursing, denouncing, or jinxing something. These antonyms could be used in different contexts such as political, social or climatic conditions. For instance, while avoiding panic, governments could downplay the threats of a natural calamity by delaying or suppressing the warning signals. In the same vein, people's negative attitudes may jinx an endeavor or a community's effort.