irregular

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Contrary to rule, accepted order, or general practice: irregular hiring practices.
2. adj. Not conforming to legality, moral law, or social convention: an irregular marriage.
3. adj. Not straight, uniform, or symmetrical: irregular facial features.
4. adj. Of uneven rate, occurrence, or duration: an irregular heartbeat.
5. adj. Deviating from a type; atypical.
6. adj. Botany Having differing floral parts, as of a zygomorphic or asymmetrical flower.
7. adj. Falling below the manufacturer's standard or usual specifications; imperfect.
8. adj. Grammar Departing from the usual pattern of inflection, derivation, or word formation, as the present forms of the verb be or the plural noun children.
9. adj. Not belonging to a permanent, organized military force: irregular troops.
10. n. One, such as an item of merchandise, that is irregular.
11. n. A soldier, such as a guerrilla, who is not a member of a regular military force.

Century Dictionary and Cyclopedia

1. Not regular; lacking regularity or method in some respect; not conformable to rule, order, symmetry, uniformity, or a fixed principle; deviating from the normal or usual course or state; devious; unmethodical; uneven: as, an irregular figure, outline, or surface; irregular verbs; irregular troops.
2. Not regular in action or method; not conformed or conforming to regular rules or principles; hence, disorderly; lawless; improper: as, he is given to irregular courses.
3. Specifically In human anatomy, being of no determinate shape, as a vertebra: said only of bones. Bones were formerly classed unnaturally in four categories, long, short, flat, and irregular. Most bones fall in the last-named category.
4. In zoology: Not having a definite form; bilaterally or radially unsymmetrical; not having the form usual in a group; differing in an unusual manner from neighboring parts: as, an irregular third joint of an insect's antenna.
5. Not arranged in a definite manner, or varying in position or direction: as, irregular marks (that is, marks varying in size or distance from one another); irregular punctures or striæ.
6. In echinoderms, not exhibiting radial symmetry; exocyclic or petalostichous; spatangoid or clypeastroid: specifically said of the heart-urchins and other sea-urchins of the division Irregularia. See cut under petalostichous.
7. In botany, not having all the members of the same part alike: said of flowers. An irregular flower is one in which the members of some or all of its floral circles—for example, petals—differ from one another in size, shape, or extent of union, as in the bean, the violet, and the larkspur. The term is also used less specifically, and is often not discriminated from unsymmetrical.
8. n. One who is not subject or does not conform to established regulations; especially, a soldier who is not in regular service, or a person practising medicine without belonging to the regular profession.

Wiktionary

1. adj. Nonstandard; not conforming to rules or expectations.
2. adj. Of a surface, rough.
3. n. A soldier who is not a member of an official military force and, often, does not follow regular army tactics.

GNU Webster's 1913

1. adj. 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
2. n. One who is not regular; especially, a soldier not in regular service.

WordNet 3.0

1. adj. independent in behavior or thought
2. adj. (used of the military) not belonging to or engaged in by regular army forces
3. adj. lacking continuity or regularity
4. adj. falling below the manufacturer's standard
5. adj. (of solids) not having clear dimensions that can be measured; volume must be determined with the principle of liquid displacement
6. adj. (of a surface or shape); not level or flat or symmetrical
7. n. a member of an irregular armed force that fights a stronger force by sabotage and harassment
8. adj. deviating from normal expectations; somewhat odd, strange, or abnormal
9. adj. not occurring at expected times
10. n. merchandise that has imperfections; usually sold at a reduced price without the brand name
11. adj. contrary to rule or accepted order or general practice