expansion

Etymology

From French expansion, from Latin expānsiō. Surface analysis: expand + -sion.

noun

1. An act, process, or instance of expanding.
   1. The fractional change in unit length per unit length per unit temperature change.
      Look up the expansion of 1018 steel at stick welding temps and figure out how far this thing's gonna bend once we weld it up.
   2. (building) A new addition.
      My new office is in the expansion behind the main building.
   3. A product to be used with a previous product.
      This expansion requires the original game board.
   4. That which is expanded; expanse; extended surface.
      Mother of mighty Rome's imperial line, / Delight of man, and of the powers divine, / Venus, all-bounteous queen! whose genial power / Diffuses beauty in unbounded store / Through seas, and fertile plains, and all that lies / Beneath the starred expansion of the skies. a. 1804, James Beattie, “The Beginning of the First Book of Lucretius”, in The Poetical Works of James Beattie (The Aldine Edition of the British Poets), London: Bell and Daldy[…], published 1866, →OCLC, pages 170–171
   5. (steam engines) The operation of steam in a cylinder after its communication with the boiler has been cut off, by which it continues to exert pressure upon the moving piston.
   6. (writing, editing, audio content) The replacement of a short name (e.g., acronym, initialism, alphanumeric symbol, abbreviation) with the longer name that is synonymous with it, as when spelling out acronyms to ensure clarity for a general audience.
      Expansion of acronyms is often helpful for nonexpert readers (anacronyms excluded).
      1. The string of text thus substituted.
         The acronym "FNDs" can mean either "functional neurologic disorders" or "focal neurologic deficits", so you'd better use the expansion instead of the acronym, for clarity in this context; readers of this paragraph may not have read, or remember, which definition you used 40 pages earlier.