Synonyms for Antonymous (same or very similar meaning)
WordNet sense 1 (of words so related that one reverses the relation denoted by the other):
converse, converse
WordNet sense 2 (of words or propositions so related that both cannot be true but both may be false):
contrary, contrary
WordNet sense 3 (of words or propositions so related that both cannot be true and both cannot be false):
contradictory
From the ODE community, based on WordNet
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