a combining form with the meaning “ray, beam,” used in the formation of compound words, with the particular senses “radiation” in the physical sciences (actinometer) and “having raylike structures,” “radiate in form” in biology (actinomyces; actinopod).
Also especially before a vowel, actin-.

Origin of actino-

< Greek, combining form representing aktī́s (genitive aktînos) ray, beam; see -o- Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

British Dictionary definitions for actino-


before a vowel actin-

combining form

indicating a radial structureactinomorphic
indicating radioactivity or radiationactinometer

Word Origin for actino-

from Greek aktino-, from aktis beam, ray
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

Medical definitions for actino-



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