Runtish, an adjective used to describe something that is small or undersized, has several antonyms that denote qualities of being big or larger than average. These antonyms include imposing, massive, towering, substantial, enormous, and colossal. These antonyms can be used to describe anything from a hulking building to a towering tree or a massive animal. Other antonyms for runtish may include words such as stout, broad, sturdy, and bulky, all of which signify strength, size, and power. Whether it's a towering skyscraper, a massive elephant, or a broad-shouldered athlete, these words are the opposite of runtish in every way.