Halfpint is a term used to refer to a small person or a small quantity of something. The antonyms of halfpint would be words that indicate largeness or a greater amount. For example, the antonym for a small person would be big, large or tall. For a small quantity of something, the antonym could be a gallon, a barrel, or a bucket. Whereas words such as huge, enormous, colossal, or mammoth would be antonyms of halfpint indicating a tremendous quantity or size of something. Thus, antonyms of halfpint can help to convey a sense of magnitude or scale in words.