self-conceit 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.

late 14c., "a thought, a notion, that which is mentally conceived," from conceiven (see conceive) based on analogy of deceit/deceive and receipt/receive. The sense evolved from "something formed in the mind" to "fanciful or witty notion, ingenious thought" (1510s), to "vanity, exaggerated estimate of one's own mental abilities" (c. 1600) through shortening of self-conceit (1580s).

A doublet of concept, it sometimes was spelled conceipt in Middle English. Sometimes the Italian form concetto (plural concetti) was used in English 18c.-19c. for "piece of affected wit;" OED describes it as "a term originally proper to Italian literature."