irregular

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. [...] ’”

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.”

   “Near by, where the crystal clear River Llugwy is crossed by a bridge, stands a small and ancient church built of massive, irregular boulders.”

   “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.”

   “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.”

   “The improvements will be most keenly felt across Lincolnshire, where current irregular service patterns are more a function of operational convenience than passenger demand.”

4. Of a polygon, not regular; having sides that are not equal or angles that are not equal.
5. Of a polyhedron, whose faces are not all regular polygons (or are not equally inclined to each other).
6. 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".”

   “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.”