Most two by four is a size designation for a specific type of lumber used in construction. However, there are several antonyms for this phrase, which could be used to describe alternative types of lumber, such as thin, narrow, or lightweight options. Conversely, some antonyms for most two by four could be thick, wide, or heavy- indicating larger, stronger or more durable types of lumber. Depending on the specific context, the antonym of most two by four can vary greatly. Ultimately, the choice of antonym will depend on the desired attributes needed for the specific construction project, such as structural integrity or budget constraints.