[ik-span-shuh n]
  1. the act or process of expanding.
  2. the state or quality of being expanded.
  3. the amount or degree of expanding.
  4. an expanded, dilated, or enlarged portion or form of a thing: The present article is an expansion of one he wrote last year.
  5. anything spread out; expanse.
  6. Mathematics.
    1. the development at length of an expression indicated in a contracted form, as a2 + 2ab + b2 for the expression (a + b)2.
    2. any mathematical series that converges to a function for specified values in the domain of the function, as 1 + x + x2 + … for 1/(1 − x) when x < 1.
  7. Machinery. that part of the operation of an engine in which the volume of the working medium increases and its pressure decreases.
  8. an increase in economic and industrial activity (opposed to contraction).
  9. additional content for a video game, card game, board game, etc., that significantly expands or alters the way the game is played: I really improved my deck with cards from the latest expansion. You can play the stand-alone expansion without ever buying the original game.

Origin of expansion

1605–15; < Late Latin expānsiōn- (stem of expānsiō) a spreading out. See expanse, -ion
Related formsex·pan·sion·al, adjectivean·ti·ex·pan·sion, adjectivenon·ex·pan·sion, nouno·ver·ex·pan·sion, nounpre·ex·pan·sion, nounre·ex·pan·sion, nounself-ex·pan·sion, nounsu·per·ex·pan·sion, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for overexpansion


  1. an excessive increase, enlargement, or development, esp in the activities of a company


  1. the act of expanding or the state of being expanded
  2. something expanded; an expanded surface or part
  3. the degree, extent, or amount by which something expands
  4. an increase, enlargement, or development, esp in the activities of a company
  5. maths
    1. the form of an expression or function when it is written as the sum or product of its terms
    2. the act or process of determining this expanded form
  6. the part of an engine cycle in which the working fluid does useful work by increasing in volume
  7. the increase in the dimensions of a body or substance when subjected to an increase in temperature, internal pressure, etc
Derived Formsexpansionary, adjective
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 overexpansion



1610s, "anything spread out;" 1640s, "act of expanding," from French expansion, from Late Latin expansionem (nominative expansio) "a spreading out," noun of action from past participle stem of Latin expandere (see expand).

Online Etymology Dictionary, © 2010 Douglas Harper

overexpansion in Medicine


  1. An increase in size.
  2. The spreading out of a structure, such as a tendon.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

overexpansion in Science


  1. An increase in the volume of a substance while its mass remains the same. Expansion is usually due to heating. When substances are heated, the molecular bonds between their particles are weakened, and the particles move faster, causing the substance to expand.
  2. A number or other mathematical expression written in an extended form. For example, a2 + 2ab + b2 is the expansion of (a + b)2.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.