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[ak-tuh n] /ˈæk tən/
noun, Biochemistry
a globulin that is present in muscle plasma and that in connection with myosin plays an important role in muscle contraction.
Origin of actin
1940-45; perhaps act + -in2


variant of actino- before a vowel:
actinism. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for actin
Historical Examples
  • And if Mr. Robert hadn't been actin' so much like a poor prune he'd have quit that line right there.

    Torchy, Private Sec. Sewell Ford
  • You're actin' square by my poor gal, sir, so I'm agoin' to act square by you.

    The Bishop's Secret Fergus Hume
  • "You're actin' a leetle nervous your own self, man," said Tom Osby, keenly.

    Heart's Desire Emerson Hough
  • All the time Myrtle was leanin' against ma, just like a cat, actin', I thought.

    Mitch Miller Edgar Lee Masters
  • And there wa'n't any special reason that I could see for her actin' that way.

  • This is altruism, an' we're but actin' out what you been preachin'.

    A Voice in the Wilderness Grace Livingston Hill
  • "I don't know as I was actin' right, either, to talk as I did," she continued abruptly.

    While Caroline Was Growing Josephine Daskam Bacon
  • I was only actin' the lions and a den of hyenas in them days.

  • The nigher we got, the harder he stared; and the man in front was actin' similar in regards to him.

    The Depot Master Joseph C. Lincoln
  • That's what my boys was brought up to think, 'n they're actin' accordin'.

    Peak and Prairie Anna Fuller
British Dictionary definitions for actin


a protein that participates in many kinds of cell movement, including muscle contraction, during which it interacts with filaments of a second protein, myosin
Word Origin
C20: from act + -in
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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actin in Medicine

actin ac·tin (āk'tĭn)
One of the protein components found in muscle, existing as F-actin or G-actin, into which actomyosin can be split and which acts with myosin in muscle contraction.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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actin in Science
A protein found in all eukaryotic cells, forming filaments that make up a main component of the cell's supporting matrix or cytoskeleton. Actin and the protein myosin together make up the contractile units (called sarcomeres) of skeletal muscle fibers.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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