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[oh-pee-oid] /ˈoʊ piˌɔɪd/
noun, Biochemistry, Pharmacology
any opiumlike substance.
any of a group of natural substances, as the endorphins, produced by the body in increased amounts in response to stress and pain.
any of several synthetic compounds, as methadone, having effects similar to natural opium alkaloids and their derivatives.
pertaining to such a substance.
Origin of opioid
1955-60; opi(um) + -oid Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for opioid
  • That's good, because fat activates the brain's natural mu-opioid receptors, provoking what scientists call a hedonic response.
  • Morphine acts on a part of the brain known as the opioid system, which is linked to pain, pleasure and addictive behaviors.
  • Natural pain moderation depends on the activation of a brain cell surface protein called the mu-opioid receptor.
  • It is no more neurotoxic than any other opiate, or the opioid substances produced in the brain naturally.
  • The concept of entero-colonic encephalopathy, autism and opioid receptor ligands.
  • During the intense cross-examination, he remained calm as he methodically explained his opioid treatments.
  • Naltrexone helps lessen cravings and mutes the pleasurable effects of alcohol by blocking opioid receptors in the brain.
  • Individuals with opioid addiction often experience serious withdrawal symptoms that may make relapse unavoidable.
British Dictionary definitions for opioid


  1. any of a group of substances that resemble morphine in their physiological or pharmacological effects, esp in their pain-relieving properties
  2. (modifier) of or relating to such substances: opioid receptor, opioid analgesic
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
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Word Origin and History for opioid

1957, from opium + -oid.

Online Etymology Dictionary, © 2010 Douglas Harper
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opioid in Medicine

opioid o·pi·oid (ō'pē-oid')
See opiate. adj.

o'pi·oid' adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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