irregular

Etymology

From Middle English irreguler, from Old French irreguler, from Medieval Latin or Late Latin irrēgulāris, from in- + regularis, equivalent to ir- + regular.

adj

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, 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
   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. 2013-01-01, 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. 2013-07-19, 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, of a polygon) not regular; having sides that are not equal or angles that are not equal
5. (geometry, of a polyhedron) whose faces are not all regular polygons (or are not equally inclined to each other)
6. (grammar, of a word) not following the regular or expected patterns of inflection in a given language
   "Calves", "cacti", and "children" are irregular plurals.
   I hate learning all the irregular conjugations in French.

noun

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