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nor-

  1. a combining form used in the names of chemical compounds which are the normal or parent forms of the compound denoted by the base words: l-norepinephrine.
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Origin of nor-

short for normal
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for nor-

nor-

combining form
  1. indicating that a chemical compound is derived from a specified compound by removal of a group or groupsnoradrenaline
  2. indicating that a chemical compound is a normal isomer of a specified compound
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Word Origin

by shortening from normal
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

nor- in Medicine

nor-

pref.
  1. A precursor compound that differs from its successor by the absence of a radical group, usually methyl:norepinephrine.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.