irregular vs casual

irregular is a noun but casual is not a noun.

Word	Noun	Adjective	Verb	Adverb
irregular	Yes	Yes	No	No
casual	No	Yes	No	No

irregular (noun)	casual (noun)
merchandise that has imperfections; usually sold at a reduced price without the brand name
a member of an irregular armed force that fights a stronger force by sabotage and harassment

irregular (adjective)	casual (adjective)
contrary to rule or accepted order or general practice	hasty and without attention to detail; not thorough
(of solids) not having clear dimensions that can be measured; volume must be determined with the principle of liquid displacement	not showing effort or strain
(used of the military) not belonging to or engaged in by regular army forces	occurring on a temporary or irregular basis
deviating from normal expectations; somewhat odd, strange, or abnormal	marked by blithe unconcern
failing to meet a standard of manufacture due to an imperfection	appropriate for ordinary or routine occasions
lacking continuity or regularity	occurring or appearing or singled out by chance
not occurring at a regular rate or fixed intervals	natural and unstudied
independent in behavior or thought	characterized by a feeling of irresponsibility
(of a surface or shape); not level or flat or symmetrical	without or seeming to be without plan or method; offhand