introjection n.

word-forming element, from Latin intro (adv.) "in, on the inside, within, to the inside," from PIE *en-t(e)ro-, suffixed form of root *en "in."

late 15c., projeccioun, in alchemy, "transmutation by casting a powder on molten metal," from Old French projeccion and directly from Latin proiectionem (nominative proiectio) "a throwing forward, a stretching out," noun of action from past-participle stem of proicere "stretch out, throw forth" (see project (v.)).

From 1560s in the cartographical sense of "system of continuous correspondence between the points of a spherical surface and those of a plane." From 1590s as "action of projecting." From 1756 as "that which projects or juts out."