• synonyms


[ak-tuh n]
noun Biochemistry.
  1. a globulin that is present in muscle plasma and that in connection with myosin plays an important role in muscle contraction.
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Origin of actin

1940–45; perhaps act + -in2


  1. variant of actino- before a vowel: actinism.
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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for actin

Historical Examples of actin

  • "The mare's actin' as if she'd a cup of tea, too," muttered her companion, Ned.


    W. A. Fraser

  • And yet, if she wanted Jonadab, she was actin' mighty funny.

    The Depot Master

    Joseph C. Lincoln

  • 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

  • All I should be able to think of was what she wore, or didn't wear, when she was actin' her parts.

    Kent Knowles: Quahaug

    Joseph C. Lincoln

  • Your Uncle Zoeth and me have been actin' as your pilots for a consider'ble spell.


    Joseph C. Lincoln

British Dictionary definitions for actin


  1. a protein that participates in many kinds of cell movement, including muscle contraction, during which it interacts with filaments of a second protein, myosin
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Word Origin for actin

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

actin in Medicine


  1. 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.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

actin in Science


  1. 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.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.