self-possession (n.)

word forming element indicating "oneself," also "automatic," from Old English use of self (pron.) in compounds, such as selfbana "suicide," selflice "self-love, pride, vanity, egotism," selfwill "free will." Middle English had self-witte "one's own knowledge and intelligence" (early 15c.).

OED counts 13 such compounds in Old English. Middle English Compendium lists four, counting the self-will group as a whole. It re-emerges as a living word-forming element mid-16c., "probably to a great extent by imitation or reminiscence of Greek compounds in (auto-)," and formed a great many words in the pamphlet disputes of the 17c.

mid-14c., possessioun, "act or fact of holding, occupying, or owning; a taking possession, occupation," also "thing possessed, that which is possessed, material or landed property" (in plural, goods, lands, or rights owned), from Old French possession "fact of having and holding; what is possessed;" also "demonic possession," and directly from Latin possessionem (nominative possessio) "a seizing, possession," noun of action from past-participle stem of possidere "to possess" (see possess).

The legal property sense is earliest; the demonic sense in English, "state of being under the control of evil spirits or of madness," first is recorded 1580s. Phrase possession is nine (or eleven) points of the law is out of a supposed 10 (or 12). With eleven from 1640s; with nine from 1690s.

St. Jerome in his 'Life of St. Hilarion' has given us a graphic account of the courage with which that saint confronted, and the success with which he relieved, a possessed camel. [W.E.H. Lecky, "A History of European Morals," 1869]