Being tantamount refers to something that is equivalent or equal in value or meaning. Antonyms for this phrase would therefore be words that indicate lack of equivalence, inequality, or dissimilarity. Some possible antonyms include unequal, incomparable, disparate, dissimilar, unrelated, different, unalike, dissimilar, distinct, and non-equivalent. These words convey the idea that something is not equal or equivalent to something else, and may even indicate contrast, divergent qualities, or significant differences between two or more things. By using antonyms, writers can create a sense of differentiation, contrast, or even opposition between two or more ideas or concepts.