S: (adj) antagonistic, incompatible (used especially of drugs or muscles that counteract or neutralize each other's effect)
S: (adj) uncongenial, incompatible (not suitable to your tastes or needs) "the uncongenial roommates were always fighting"; "the task was uncongenial to one sensitive to rebuffs"
S: (adj) incompatible (incapable of being used with or connected to other devices or components without modification)
S: (adj) contrastive, incompatible (of words so related that one contrasts with the other) "`rich' and `hard-up' are contrastive terms"