word-forming element indicating "branch of knowledge, science," now the usual form of -logy. Originally used c. 1800 in nonce formations (commonsensology, etc.), it gained legitimacy by influence of the proper formation in geology, mythology, etc., where the -o- is a stem vowel in the previous element.

The second element is prop[erly] -logy (-logue, etc.), the -o- belonging to the preceding element; but the accent makes the apparent element in E[nglish] to be -ology, which is hence often used as an independent word. [Century Dictionary] 
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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" [Weekley]. Another adjective was abnormous (1742) "irregular, misshapen," from Latin abnormis. Related: Abnormally.

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normal (adj.)

c. 1500, "typical, common;" 1640s, in geometry, "standing at a right angle, perpendicular," from Late Latin normalis "in conformity with rule, normal," in classical Latin "made according to a carpenter's square," from norma "rule, pattern," literally "carpenter's square," a word of unknown origin (see norm). Meaning "conforming to common standards or established order or usage, regular, usual" is attested from 1828 but probably is older than the record [Barnhart].

Meaning "heterosexual" is by 1914. As a noun meaning "usual state or condition," from 1890 (in geometry as "a perpendicular" from 1727). Sense of "a normal person or thing" is attested by 1894. Normal school "training college for teachers" (1835) is a translation of French école normale (1794), a creation of the French Republic; the notion is of "serving to set a standard." The U.S. city of Normal, Illinois, was named 1857 for the normal school established there.

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regent (n.)

c. 1400, "a ruler," from the adjective regent "ruling, governing" (late 14c., now archaic), later "exercising vicarious authority," from Old French regent and directly from Medieval Latin regentem (nominative regens), from Latin regens "ruler, governor," noun use of present participle of regere "to rule, direct" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule").

Meaning "one who rules during the minority or absence of a sovereign" is from early 15c., used in place of king as not implying legitimacy or permanence of rule. The Latin word for this was interrex (plural interreges). Sense of "university faculty member" (especially, in old universities, a master or doctor who takes part in the regular duties of instruction or government) is attested from late 14c. and preserves the older meaning.

I shall calle unto me my counceyle of my moste trusty knyghtes and deukes and regeaunte kynges and erlys and barowns. [Malory, late 15c.]
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