The word under-bellies refers to the vulnerable, weak or less favorable aspects of something. Antonyms for under-bellies would be synonyms for strength, security or positivity. Some potential antonyms for this term could include: assets, benefits, advantages, or strong points. These are all traits or characteristics that promote a sense of stability, resilience and confidence. Other potential antonyms might include attributes such as fortitude, capability, and expertise, which all connote a sense of competence, mastery, and capability. In short, while under-bellies reflect the shortcomings of a thing or concept, antonyms for this term represent the strengths and advantages of that same subject.