"obstinate, unmindful of the will or wishes of others," late 15c., from self-wille "obstinate or perverse insistence on one's own desires or opinions" (mid-14c.); see self + will (n.). Old English selfwill, selfwyll meant "free will."
Self-willedness "quality or condition of being self-willed" is from mid-15c., though it is not certain whether "obstinacy" or "self-reliance" is implied.
Middle English also had an adjective self-willy (15c.), and the adverb self-willes is attested from late 12c. as "willingly, voluntarily;" late 14c. as "willfully, stubbornly."
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]
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.