WordNet sense 1 (a member of an irregular armed force that fights a stronger force by sabotage and harassment):

guerilla, guerrilla, insurgent

WordNet sense 2 (merchandise that has imperfections; usually sold at a reduced price without the brand name):

second

WordNet sense 3 (not conforming to legality, moral law, or social convention):

improper, unconventional

WordNet sense 4 (occuring from time to time):

casual, occasional

WordNet sense 5 (irregular in shape or outline):

crooked, crooked

WordNet sense 6 (deviating from normal expectations; somewhat odd, strange, or abnormal):

atypical

WordNet sense 7 (not normal; not typical or usual or regular or conforming to a norm):

abnormal

WordNet sense 8 (lacking continuity or regularity):

temporary

WordNet sense 9 (involving less than the standard or customary time for an activity):

part-time

WordNet sense 10 (not even or uniform as e.g. in shape or texture):

uneven

WordNet sense 11 (independent in behavior or thought):

maverick, unorthodox

WordNet sense 12 (not occurring at expected times):

unpredictable

WordNet sense 13 (recurring in scattered and irregular or unpredictable instances):

sporadic