word-forming element meaning "outside; beyond the scope of; in addition to what is usual or expected," in classical Latin recorded only in extraordinarius, but more used in Medieval Latin and modern formations; it represents Latin extra (adv.) "on the outside, without, except," the old fem. ablative singular of exterus "outward, outside," comparative of ex "out of" (see ex-).
1670s, "action of closely inspecting or examining," noun of action from past participle stem of Latin introspicere "to look into, look at, examine, observe attentively," from intro- "inward" (see intro-) + specere "to look at" (from PIE root *spek- "to observe"). Meaning "action of searching one's feelings or thoughts" is from 1807.