Chief constituents refer to the main components of a substance or entity. The antonyms of this term would therefore refer to the minor or lesser components that make up a substance. These could be described as nonessential or secondary constituents. Other antonyms might include subsidiary, supplementary, or peripheral constituents, which serve a supporting or ancillary role. In contrast to the chief constituents that give a substance its essential qualities and characteristics, these minor components may have a less significant impact on the substance's overall properties, but nevertheless play an important role in defining its character and makeup.