1580s, "action of distorting; state of being twisted out of shape," from Latin distortionem (nominative distortio), noun of action from past-participle stem of distorquere "to twist different ways, distort," from dis- "completely" (see dis-) + torquere "to twist" (from PIE root *terkw- "to twist").
Figurative use (of words, etc.), "a perversion of the true meaning or intent" is from 1640s. Meaning "change in the wave-form of a signal by an electronic device" is from 1887, specifically of amplifiers by 1962.
c. 1300, retrete, "a step backward;" late 14c., "act of retiring or withdrawing; military signal for retiring from action or exercise," from Old French retret, retrait, noun use of past participle of retrere "draw back," from Latin retrahere "draw back, withdraw, call back," from re- "back" (see re-) + trahere "to draw" (see tract (n.1)).
Meaning "place of seclusion" is from early 15c.; sense of "establishment for mentally ill persons" is from 1797. Meaning "period of retirement for religious self-examination" is from 1756.
early 13c., "gesture or motion of the hand," especially one meant to communicate something, from Old French signe "sign, mark," from Latin signum "identifying mark, token, indication, symbol; proof; military standard, ensign; a signal, an omen; sign in the heavens, constellation."
According to Watkins, literally "standard that one follows," from PIE *sekw-no-, from root *sekw- (1) "to follow." But de Vaan has it from PIE *sekh-no- "cut," from PIE root *sek- "to cut" He writes: "The etymological appurtenance to seco 'to cut' implies a semantic shift of *sek-no- 'what is cut out', 'carved out' > 'sign'." But he also also compares Hebrew sakkin, Aramaic sakkin "slaughtering-knife," and mentions a theory that "both words are probably borrowed from an unknown third source."
It has ousted native token. Meaning "a mark or device having some special importance" is recorded from late 13c.; that of "a miracle" is from c. 1300. Zodiacal sense in English is from mid-14c. Sense of "characteristic device attached to the front of an inn, shop, etc., to distinguish it from others" is first recorded mid-15c. Meaning "token or signal of some condition" (late 13c.) is behind sign of the times (1520s). In some uses, the word probably is a shortening of ensign. Sign language is recorded from 1847; earlier hand-language (1670s).
Old English had the adverb bæcling. As an adjective, from 1550s. Meaning "behindhand with regard to progress" is first attested 1690s. To ring bells backward (from lowest to highest), c. 1500, was a signal of alarm for fire or invasion, or to express dismay. Another Middle English word for "backward, wrongly" was arseward (c. 1400); Old English had earsling.