Antonyms for the word "square-built" include words like "slender," "small," "narrow," and "frail." Such words describe a person or object that is thin, delicate, and not sturdy. Other antonyms for "square-built" include "curvy," "round," and "bulbous," which all suggest a shape that is curved, plump, or irregular. These opposites of "square-built" evoke a different set of imagery and feelings than the original word, which is often associated with strength, solidity, and stability. Using antonyms can help writers add variety and nuance to their descriptions, making their writing more engaging and vivid.