occasional vs irregular

occasional is not a noun while irregular is a noun.

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

occasional (noun)	irregular (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

occasional (adjective)	irregular (adjective)
occurring from time to time	contrary to rule or accepted order or general practice
occurring on a temporary or irregular basis	(of solids) not having clear dimensions that can be measured; volume must be determined with the principle of liquid displacement
recurring or reappearing from time to time	(used of the military) not belonging to or engaged in by regular army forces
occurring or appearing at usually irregular intervals	deviating from normal expectations; somewhat odd, strange, or abnormal
	failing to meet a standard of manufacture due to an imperfection
	lacking continuity or regularity
	not occurring at a regular rate or fixed intervals
	independent in behavior or thought
	(of a surface or shape); not level or flat or symmetrical