Etymology
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inside (n.)

late 14c., ynneside "interior part (of the body)," compound of in (prep.) + side (n.). General sense "inner side or part (of anything)" is from c. 1500.

The adjective sense "being on the inside" is from 1610s, from the noun. It began to be used in slang c. 1900 in reference to the supposed real facts or situation that only an insider would know. Inside man is from 1911 (originally in reference to workers used by management to sniff out union activity); inside job "robbery, espionage, etc., committed by or with the help of a resident or servant of a place" is attested by 1887, American English (also, late 19c., early 20c., "indoors work").

The figurative inside track "advantage" (1854) however is a metaphor from horse racing (1830); inside lanes are shorter than the outer ones on a curved track. Adverbial use in American English inside of (in reference to time) is from 1839.

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inside-out (adj.)

"with the in side being out," c. 1600, from inside (n.) + out (prep.). Reverse in form but identical in sense outside-in is attested by 1771.

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insider (n.)
"one in possession of special information by virtue of being within some organization," 1848, from inside (n.) + -er (1). Originally in reference to the stock markets.
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intro- 
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."
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intra- 
word-forming element meaning "within, inside, on the inside," from Latin preposition intra "on the inside, within, in, into;" of time, "during, in the course of," related to inter "between," from PIE *en-t(e)ro-, from root *en "in." Commonly opposed to extra-, and compare inter-. The use of intra as a prefix was rare in classical Latin.
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within (adv., prep.)
Old English wiðinnan "within, from within," literally "against the inside," see with + in.
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emic (adj.)

"of or pertaining to analysis of cultural phenomena from the inside," 1954, from phonemic.

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intra-cellular (adj.)
also intracellular, "existing or happening inside a cell," 1842; see intra- "within" + cellular.
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ento- 
word-forming element used chiefly in biology and meaning "within, inside, inner," from Greek ento-, combining form of entos (adv., prep.) "within, inside," as a noun, "inner parts" (cognate with Latin intus), from PIE *entos-, extended form of root *en "in," with adverbial suffix *-tos, denoting origin.
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extroversion (n.)
mid-17c., "condition of being turned inside out," noun of action from obsolete verb extrovert (v.) "to turn inside out," from extro- + Latin vertere "to turn" (from PIE root *wer- (2) "to turn, bend"). Earliest as a word in mysticism; modern use in psychology attested by 1920.
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