WordNet sense 1 (vote against; refuse to endorse; refuse to assent):

blackball, veto

WordNet sense 2 (having a negative electric charge):

electronegative

WordNet sense 3 (not indicating the presence of microorganisms or disease or a specific condition):

disconfirming

WordNet sense 4 (on the negative side or lower end of a scale):

minus

WordNet sense 5 (indicating opposition or resistance):

antagonistic

WordNet sense 6 (designed or tending to discredit, especially without positive or helpful suggestions):

damaging

WordNet sense 7 (constituting a disadvantage):

disadvantageous, harmful