malcontent
[noun]
Synonyms: troublemaker, agitator, mischief-maker, rebel, stirrer (informal)

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Related Words: alienated, disaffected, estranged, disobedient, ungovernable, unruly, restless, contumacious, factious, insubordinate, mutinous, rebellious, seditious

[TahlilGaran] English Synonym Dictionary ▲

mal‧con‧tent /ˈmælkəntent $ ˌmælkənˈtent/ noun [countable]
formal someone who is likely to cause trouble because they are not happy with the way things are organized – used in order to show disapproval

[TahlilGaran] Dictionary of Contemporary English ▲