Irregular, a.
Etymology: [Pref. ir- not + regular: cf. F. irrégulier.]
Not regular; not conforming to a law, method, or usage recognized 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.
Syn. -- Immethodical; unsystematic; abnormal; unnatural; anomalous; erratic; devious; crooked; eccentric; unsettled; uneven; variable; changeable; mutable; desultory; disorderly; wild; immoderate; intemperate; inordinate; vicious.
1 other Webster entry under this spelling
Irregular, n.
One who is not regular; especially, a soldier not in regular service.
Shades of meaning
Fernald lists irregular only as an antonym, under horizontal, normal.
He lists it without comment; the entries above explain its neighbors.