malcontent

Short definition from Wiktionary

Adjective

1. 1
   Dissatisfied with current conditions; disaffected, discontented, rebellious.

Noun

1. 1
   A person who is not satisfied with current conditions; a discontented person, a rebel.
2. 2
   A state of discontentment or dissatisfaction; something that causes discontent.

Verb

1. 1
   To cause discontent or dissatisfaction.