Etymology
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irregular (adj.)
late 14c., "not in conformity with Church rules," from Old French irreguler "irregular, incapable, incompetent" (13c., Modern French irrégulier), from Medieval Latin irregularis "not regular," from assimilated form of in- "not, opposite of" (see in- (1)) + Latin regularis "having rules" (see regular (adj.)). General sense of "not conforming to regular rules or principles" is from late 15c. "It expresses the fact of being out of conformity with rule, but implies nothing more with certainty. Yet the word is sometimes used in a sinister sense, as though it were a euphemism for something worse." [Century Dictionary] Meaning "unsymmetrical" is from 1580s. In reference to variable stars, from 1797.
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irregular (n.)

"one not belonging to a regular body" of any sort, "one not subject to or not conforming with established regulations," 1610s, from irregular (adj.). Main modern sense of "a soldier not of the regular army" is from 1747.

Doubtless, the life of an Irregular is hard; but the interests of the Greater Number require that it shall be hard. If a man with a triangular front and a polygonal back were allowed to exist and to propagate a still more Irregular posterity, what would become of the arts of life? Are the houses and doors and churches in Flatland to be altered in order to accommodate such monsters? [Edwin Abbot, "Flatland: A Romance of Many Dimensions," 1885]
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irregularity (n.)
early 14c., "violation of Church rules governing admission to clerical office," from Old French irregularité (14c.) and directly from Medieval Latin irregularitas "irregularity," from irregularis "not regular" (see irregular (adj.)). Meaning "that which is irregular" is from late 15c.; sense of "state of non-conformity to rule" is from 1590s; meaning "want of symmetry" is from 1640s.
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vial (n.)
late 14c., vyol, an irregular variant of fyole (see phial).
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abnormal (adj.)
Origin and meaning of abnormal

"not conformed or conforming to rule, deviating from a type or standard, contrary to system or law, irregular, unnatural," 1835, a refashioning of anormal (q.v.) under influence of Latin abnormalis "deviating from a fixed rule, irregular," from ab "off, away from" (see ab-) + norma "rule" (see norm).

The older form was from French anormal (13c.), from Medieval Latin anormalus, an altered (by association with norma) borrowing of Greek anomalos "uneven, irregular," from an- "not" (see an- (1)) + homalos "even," from homos "same" (from PIE root *sem- (1) "one; as one, together with"). Compare anomaly. "Few words show such a series of pseudo-etymological perversions." Another adjective was abnormous (1742) "irregular, misshapen," from Latin abnormis. Related: Abnormally.

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indirection (n.)
"irregular means, deceitful action," 1590s, from indirect + -ion.
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malformation (n.)

also mal-formation, "faulty formation, irregular or anomalous structure," 1731, from mal- + formation.

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varicella (n.)
"chicken-pox," medical Latin, 1764, irregular diminutive of variola (see variola). Related: Varicellous.
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anomaly (n.)
Origin and meaning of anomaly

1570s, "unevenness;" 1660s, "deviation from the common rule," from Latin anomalia, from Greek anomalia "inequality," abstract noun from anomalos "uneven, irregular," from an- "not" (see an- (1)) + homalos "even," from homos "same" (from PIE root *sem- (1) "one; as one, together with"). From 1722 as "something abnormal or irregular."

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amniotic (adj.)
1822, from amnion + -ic, perhaps from or based on French amniotique. The form is irregular; a classically correct word would be *amniac.
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