Irregular
Part of speech: adjective
Definition: Nonstandard; not conforming to rules or expectations. Of a surface, rough.
Part of speech: noun
Definition: A soldier who is not a member of an official military force and, often, does not follow regular army tactics
Example sentence: But since the middle of the century in particular, the music has become very irregular in rhythm.
Insurgent
Part of speech: noun
Definition: A rebel, guerrilla, freedom fighter.
Part of speech: adjective
Definition: rebellious, opposing authority