Meaning

• A soldier who is not a member of an official military force and, often, does not follow regular army tactics

• One who does not regularly attend a venue

Meaning

• Nonstandard; not conforming to rules or expectations

• (of a surface) rough

• Without symmetry, regularity, or uniformity

• (of a polygon) not regular; having sides that are not equal or angles that are not equal

• (of a polyhedron) whose faces are not all regular polygons (or are not equally inclined to each other)

• (grammar, of a word) not following the regular or expected patterns of inflection in a given language

  ""Calves", "cacti", and "children" are irregular plurals."