early 15c., "contortion, twisting, distortion; a disorder characterized by contortion," from Old French torture "infliction of great pain; great pain, agony" (12c.), and directly from Late Latin tortura "a twisting, writhing," in Medieval Latin "pain inflicted by judicial or ecclesiastical authority as a means of punishment or persuasion," from stem of Latin torquere "to twist, turn, wind, wring, distort" (from PIE root *terkw- "to twist").
The meaning "infliction of severe bodily pain as a means of punishment or persuasion" in English is from 1550s. The theory behind judicial torture was that a guilty person could be made to confess, but an innocent one could not, by this means. Macaulay writes that it was last inflicted in England in May 1640.
Old English self, sylf (West Saxon), seolf (Anglian), "one's own person, -self; own, personal; same, identical," from Proto-Germanic *selbaz (source also of Old Norse sjalfr, Old Frisian self, Dutch zelf, Old High German selb, German selb, selbst, Gothic silba), Proto-Germanic *selbaz "self," from PIE *sel-bho-, suffixed form of root *s(w)e-, pronoun of the third person and reflexive (referring back to the subject of a sentence), also used in forms denoting the speaker's social group, "(we our-)selves" (see idiom).
Its use as the second element in compounded reflexive pronouns (herself, etc.) was in Old English, from the original independent (and inflected) use of self following personal pronouns, as in ic selfa "myself," min selfes "of myself." With a merging of accusative, dative, and genitive cases.
As a noun from c. 1200 as "the person or thing previously specified;" early 14c. as "a person in relation to that same person." G.M. Hopkins used selve as a verb, "become or cause to become a unique self" (1880) but its use seems to have been restricted to poets.
1680s, "aware of one's action or oneself," a word of the English Enlightenment (Locke was using it by 1690, along with self-consciousness "state of being aware of oneself, consciousness of one's own identity"), from self- + conscious. The morbid sense of "preoccupied with one's own personality, conscious of oneself as an object of observation to others" is attested by 1834 (J.S. Mill). Related: Self-consciously.
[I]n law, the act of forcibly resisting a forcible attack upon one's own person or property, or upon the persons or property of those whom, by law, one has a right to protect and defend. [Century Dictionary]
in reference to things, "destroy itself automatically;" see self- + destruct, apparently first attested in the U.S. television series "Mission Impossible" (1966). Self-destructive "having the property of annulling itself" is recorded from 1650s, and self-destruction "destruction of oneself, suicide" is attested from 1580s; self-destroying (n.) is from 1610s.
1680s, "determination of mind; determination by one's own will or powers without external influence," from self- + determination. The political sense, action of a people in deciding its statehood and form of government," is attested by 1911, popularized 1918 by U.S. President Woodrow Wilson in reference to the settlement of World War I. The idea itself is from 19c., and Churchill compared Fichte's Selbst bestimmung. Related: Self-determined; self-determining.