Opppositive is not a commonly used word and it is difficult to come up with synonyms that would have the exact same meaning. However, some words that could be used interchangeably with oppositive include contrary, contradictory, opposing, and antithetical. Contrary refers to something that goes against or is the opposite of something else while contradictory means that two statements cannot both be true at the same time. Opposing means to be against something while antithetical refers to something that is the absolute opposite of something else. These words can be used depending on the context and the intended meaning in order to convey the message accurately.