casual vs irregular

casual

noun
  • A soldier temporarily at a place of duty, usually en route to another place of duty. 

  • A person whose engagement with media is relaxed or superficial. 

  • A worker who is only working for a company occasionally, not as its permanent employee. 

  • A player of casual games. 

  • Shoes suitable for everyday use, as opposed to more formal footwear. 

  • A member of a group of football hooligans who wear expensive designer clothing to avoid police attention; see casual (subculture). 

  • One who receives relief for a night in a parish to which he does not belong; a vagrant. 

adj
  • Designed for informal or everyday use. 

  • Coming without regularity; occasional or incidental. 

  • Happening or coming to pass without design. 

  • Informal; relaxed. 

  • Employed irregularly. 

  • Happening by chance. 

  • Careless. 

irregular

noun
  • A soldier who is not a member of an official military force and who may not use regular army tactics. 

  • One who does not regularly attend a venue. 

adj
  • without symmetry, regularity, or uniformity 

  • rough 

  • not regular; having sides that are not equal or angles that are not equal 

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

  • nonstandard; not conforming to rules or expectations 

  • not following the regular or expected patterns of inflection in a given language 

How often have the words casual and irregular occurred in a corpus of books? (source: Google Ngram Viewer )