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."
"not according to rule, abnormal," 1812, from French anormal, from Medieval Latin anormalus, a corruption of anomalus (from Greek anomalos "uneven, irregular;" see anomaly), as if from Latin ab "away" + norma "rule, pattern." In 20c., it was used as "an antonym of 'normal' when the association of 'abnormal', i.e. 'unhealthy', 'unnatural', would be inappropriate" [OED].
"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" [Weekley]. Another adjective was abnormous (1742) "irregular, misshapen," from Latin abnormis. Related: Abnormally.
1781, "a shoemaker, a shoemaker's apprentice," of unknown origin. It came to be used in Cambridge University slang c. 1796, often contemptuously, for "townsman, local merchant," and passed then into literary use, where by 1831 it was being used for "person of the ordinary or lower classes." Meaning "person who vulgarly apes his social superiors" is by 1843, popularized 1848 by William Thackeray's "Book of Snobs." The meaning later broadened to include those who insist on their gentility, in addition to those who merely aspire to it, and by 1911 the word had its main modern sense of "one who despises those considered inferior in rank, attainment, or taste." Inverted snob is from 1909.
Then there is that singular anomaly, the Inverted Snob, who balances a chip on his shoulder and thinks that everyone of wealth or social prominence is necessarily to be distrusted; that the rich are always pretentious and worldly, while those who have few material possessions are themselves possessed (like Rose Aylmer) of every virtue, every grace. [Atlantic Monthly, February 1922]