irregular vs opponent

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 

opponent

noun
  • One who is opposed or objects (to a policy, course of action or set of ideas). 

  • The participant who opens an academic debate by putting forward objections to a theological or philosophical thesis. 

  • One who opposes another; one who works or takes a position against someone or something; one who attempts to stop the progress of someone or something. 

  • One who opposes another in words (in a dispute, argument or controversy). 

  • One who opposes another physically (in a fight, sport, game, or competition). 

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