Word Origin & History
1392, ynneside "interior of the body," compound of inne (adv.) + side. The adj. is 1611, from the noun. Insider in the modern sense of "one in possession of special information by virtue of being within some organization" is first recorded 1848, originally in ref. to the stock markets. Inside job "robbery,
espionage, etc., committed by or with the help of a resident or servant of a place" is attested from 1908. Inside track "advantage" is metaphoric because those lanes are shorter on a curved track. Inside-out is attested from c.1600; inside of, in ref. to time, is from 1839.