late 14c., originally of weather and other physical conditions, from Latin moderatus "within bounds, observing moderation;" figuratively "modest, restrained," past participle of moderari "to regulate, mitigate, restrain, temper, set a measure, keep (something) within measure," related to modus "measure," from PIE *med-es-, from base *med- (see medical (adj.)). The notion is "keeping within due measure." In English, of persons from early 15c.; of opinions from 1640s; of prices from 1904. Related: Moderateness.
early 15c., "to abate excessiveness;" from Latin moderatus, past participle of moderari (see moderate (adj.)). Meaning "to preside over a debate" is first attested 1570s. Related: Moderated; moderating.
"one who holds moderate opinions on controversial subjects," 1794, from moderate (adj.). Related: Moderatism; -moderantism.