irregular vs crooked

irregular is a noun but crooked is not a noun.

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

irregular (noun)	crooked (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)	crooked (adjective)
contrary to rule or accepted order or general practice	having or marked by bends or angles; not straight or aligned
(of solids) not having clear dimensions that can be measured; volume must be determined with the principle of liquid displacement	not straight; dishonest or immoral or evasive
(used of the military) not belonging to or engaged in by regular army forces	irregular in shape or outline
deviating from normal expectations; somewhat odd, strange, or abnormal	having the back and shoulders rounded; not erect
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