Nonharmonic refers to something that is not in harmony or agreement with other things. The antonyms for this word, on the other hand, would be those that denote a sense of harmony, agreement, or coherence. Some possible antonyms for nonharmonic could be harmonic, melodic, musical, in tune, concordant, or coherent. These words depict a sense of unity and balance, or a state of agreement and accord. In music, for instance, harmonic refers to the chords that sound pleasing to the ear, whereas nonharmonic sounds harsh and out of place. Thus, understanding antonyms is crucial in expanding one's vocabulary and expressing ideas more effectively.