Not regular; not conforming to a law, method, or usage recognised as the general rule; not according to common form; not conformable to nature, to the rules of moral rectitude, or to established principles; not normal; unnatural; immethodical; unsymmetrical; erratic; no straight; not uniform; as, an irregular line; an irregular figure; an irregular verse; an irregular physician; an irregular proceeding; irregular motion; irregular conduct, etc. Cf. Regular. Mazes intricate, eccentric, intervolved, yet regular Then most when most irregular they seem. (Milton) Leading the men of Herefordshire to fight Against the irregular and wild Glendower. (Shak) A flowery meadow through which a clear stream murmured in many irregular meanders. (Jones)
Synonym: Immethodical, unsystematic, abnormal, unnatural, anomalous, erratic, devious, crooked, eccentric, unsettled, uneven, variable, changeable, mutable, desultory, disorderly, wild, immoderate, intemperate, inordinate, vicious.
Origin: Pref. Ir- not – regular: cf. F. Irregulier.