adjective

in opposition to a majority or official opinion.

dissentient voices were castigated as ‘hopeless bureaucrats’

dissenting,dissident,disagreeing,differing,discordant,contradicting,contrary,negative,anti-,opposing,opposed,objecting,protesting,complaining,rebellious,rebelling,revolutionary,nonconformist,non-compliant,unorthodox,recusant,heterodox,heretical,gainsaying

noun

a person who opposes a majority or official opinion.