inside of, Informal. within the space or period of: Our car broke down again inside of a mile.
    inside out,
    1. with the inner side reversed to face the outside.
    2. thoroughly; completely: She knew the work inside out.

Origin of inside

Middle English word dating back to 1350–1400; see origin at in, side1

Synonyms for inside

7. Inside, interior both refer to the inner part or space within something. Inside is a common word, and is used with reference to things of any size, small or large: the inside of a pocket. Interior, somewhat more formal, denotes the inner part or the space or regions within; it usually suggests considerable size or extent, and sometimes a richness of decoration: the interior of a country, of the earth, of a cathedral.

Antonyms for inside Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for inside of


noun (ˈɪnˈsaɪd)

the interior; inner or enclosed part or surface
the side of a path away from the road or adjacent to a wall
(also plural) informal the internal organs of the body, esp the stomach and bowels
inside of in a period of time less than; within
inside out with the inside facing outwards
know something inside out to know something thoroughly or perfectly

preposition (ˌɪnˈsaɪd)

in or to the interior of; within or to within; on the inside of

adjective (ˈɪnˌsaɪd)

on or of an interior; on the insidean inside door
(prenominal) arranged or provided by someone within an organization or building, esp illicitlythe raid was an inside job; inside information

adverb (ˌɪnˈsaɪd)

within or to within a thing or place; indoors
by nature; fundamentallyinside, he's a good chap
slang in or into prison


Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for inside of



late 14c., ynneside "interior of the body," compound of in (adv.) + side (n.). The adjective is 1610s, from the noun. 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"). Inside track "advantage" is metaphoric because those lanes are shorter on a curved track. Inside of, in reference to time, is from 1839.

Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with inside of

inside of

Within, in less than the whole of, referring especially to a period of time. For example, They promised to return it inside of a month. Although some authorities believe inside alone conveys the same meaning, the full term is widely used. [Early 1800s]


In addition to the idioms beginning with inside

  • inside of
  • inside out
  • inside track, the

also see:

  • on the inside
  • step in (inside)
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.