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.
"sacrifice of what commonly constitutes the happiness of life for the sake of duty or higher motive," 1650s; see self + sacrifice (n.). Adjective self-sacrificed attested from 1711. Related: self-sacrificing.
Self-sacrifice goes beyond self-denial in necessarily including the idea of surrender, as of comfort, inclination, time, health, while being also presumably in the line of a real duty. [Century Dictionary]