Etymology From Middle English irreguler, from Old French irreguler, from Medieval Latin or Late Latin irrēgulāris, from in- + regularis, equivalent to ir- + regular.
1
Nonstandard; not conforming to rules or expectations.
‘ “It would be most irregular Grandpa!” says Miss Cecily frowning and tapping her foot. “Well, we’re a pretty irregular family so that’s neither here nor there,” says the old man, impish like. [...] ’1967, Barbara Sleigh, Jessamy, Sevenoaks, Kent: Bloomsbury, published 1993, →ISBN, page 33:
2
Of a surface, rough.
3
Without symmetry, regularity, or uniformity.
The hovel stood in the centre of what had once been a vegetable garden, but was now a patch of rank weeds. Surrounding this, almost like a zareba, was an irregular ring of gorse and brambles, an unclaimed vestige of the original common.1944, Miles Burton, chapter 5, in The Three Corpse Trick:
Near by, where the crystal clear River Llugwy is crossed by a bridge, stands a small and ancient church built of massive, irregular boulders.1980, AA Book of British Villages, Drive Publications Ltd, page 100:
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Many of these classic methods are still used, with some modern improvements. For example, with the aid of special microphones and automated sound detection software, ornithologists recently reported […] that pine siskins (Spinus pinus) undergo an irregular, nomadic type of nocturnal migration.2013 January 1, Paul Bartel, Ashli Moore, “Avian Migration: The Ultimate Red-Eye Flight”, in American Scientist, volume 101, number 1, pages 47–48:
Irregular bedtimes may disrupt healthy brain development in young children, according to a study of intelligence and sleeping habits. ¶ Going to bed at a different time each night affected girls more than boys, but both fared worse on mental tasks than children who had a set bedtime, researchers found.2013 July 19, Ian Sample, “Irregular bedtimes may affect children's brains”, in The Guardian Weekly, volume 189, number 6, page 34:
The improvements will be most keenly felt across Lincolnshire, where current irregular service patterns are more a function of operational convenience than passenger demand.2019 October, Tony Miles, Philip Sherratt, “EMR kicks off new era”, in Modern Railways, page 58:
4
Geometry, Mathematics, Sciences Of a polygon, not regular; having sides that are not equal or angles that are not equal.
5
Geometry, Mathematics, Sciences Of a polyhedron, whose faces are not all regular polygons (or are not equally inclined to each other).
6
Grammar, Human sciences, Linguistics, Sciences Of a word, not following the regular or expected patterns of inflection in a given language.
"Calves", "cacti", and "children" are irregular plurals.
"To buy" is an irregular English verb: its past simple and past participle tense is "bought".
1 more example
I hate learning all the irregular conjugations in French.
Etymology From Middle English irreguler, from Old French irreguler, from Medieval Latin or Late Latin irrēgulāris, from in- + regularis, equivalent to ir- + regular.
1
A soldier who is not a member of an official military force and who may not use regular army tactics.
2
One who does not regularly attend a venue.
There's one neighborhood tavern where the regulars and irregulars go after a hard day to unlax and rewind, throw back a few, and just hang out - you know the one.2015, Brian Cook, Hands Across The Sea, page 190: