What's the "een" in Halloween?
1660s, past participle adjective from educate (v.). As an abbreviated way to say well-educated, attested from 1855. Educated guess first attested 1954.
mid-15c., "bring up (children), train," from Latin educatus, past participle of educare "bring up, rear, educate," which is related to educere "bring out, lead forth," from ex- "out" (see ex-) + ducere "to lead" (see duke (n.)). Meaning "provide schooling" is first attested 1580s. Related: Educated; educating.