Definitions of irregular:

• noun:   merchandise that has imperfections; usually sold at a reduced price without the brand name
• noun:   a member of an irregular armed force that fights a stronger force by sabotage and harassment
• adjective:   contrary to rule or accepted order or general practice

  Example: "Irregular hiring practices"

• adjective:   (of solids) not having clear dimensions that can be measured; volume must be determined with the principle of liquid displacement
• adjective:   used of the military; not belonging to or engaged in by regular army forces

  Example: "Irregular troops"

• adjective:   not occurring at expected times
• adjective:   independent in behavior or thought

  Example: "She led a somewhat irregular private life"

• adjective:   of a surface; not level or flat

  Example: "Walking was difficult on the irregular cobblestoned surface"

• adjective:   lacking continuity or regularity

  Example: "An irregular worker"

• adjective:   deviating from what is usual or common or to be expected; often somewhat odd or strange

  Example: "Highly irregular behavior"

• adjective:   used of independent armed resistance forces