1670s, "act of regulating; state of being reduced to order," noun of action from regulate. Meaning "a rule for management prescribed by a superior or competent authority" is from 1715. As an adjective, "having a fixed pattern; in accord with a rule or standard," by 1836. Related: Regulations.
"department of medicine which relates to the regulation of diet," 1854, from sito- used as a modern scientific word-forming element to mean "food," from Greek sitos "wheat, corn, meal; food," which is of unknown origin, + -logy.
late 14c., "fact of undergoing change," from Old French variance "change, alteration; doubt, hesitation" and directly from Latin variantia, from stem of variare "to change" (see vary). Meaning "state of disagreement" is recorded from early 15c. The U.S. zoning sense of "official dispensation from a building regulation" is recorded from 1925.
1851, "feeling of a father for his children," from paternal + -ism. By 1866 "government as by a father over his children, undue solicitude on the part of the central government for the protection of the people," specifically "excessive governmental regulation of the private affairs and business methods of the people." Related: Paternalistic (1890).
c. 1400, medical, "course of diet, exercise, etc. for sake of health; regulation of such matters as influence health," mid-15c., "act of governing," from Old French regimen (14c.) and directly from Latin regimen "rule, guidance, government, means of guidance, rudder," from regere "to rule, to direct, keep straight, guide" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule").
By 1751 in the transferred sense of "any regulation or remedy intended to produce gradual, beneficial effects." Regimen, regime, and, later, regiment (n.), all from the same Latin verb, were not always clearly distinguished in English, and as recently as late 19c. each of the first two was used even by careful writers in senses now restricted to the other.
c. 1300, "quantity, length, stature; manner, method, custom; a decision, a stipulated reward," from Old French sise, shortened form of assise "session, assessment, regulation, manner," noun use of fem. past participle of asseoir "to cause to sit," from Latin assidere/adsidere "to sit beside" (and thus to assist in the office of a judge), "sit with in counsel or office," from ad "to" (see ad-) + sedere "to sit," from PIE root *sed- (1) "to sit." The French word is probably a misdivision of l'assise as la sise.
The sense of "extent, amount, volume, magnitude" is from the notion of regulation (of weights, food portions, etc.) by fixing the amount of it. The specific sense of "one of a set of regularly increasing dimensions of a manufactured article for sale" is attested from 1590s (in reference to shoes). Figurative use of the sales clerk's try (something) on for size (to see if it "fits") is by 1956.