Try Our Apps


Avoid these words. Seriously.


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 Dictionary, © Random House, Inc. 2018.
Cite This Source
British Dictionary definitions for actino-


combining form
indicating a radial structure: actinomorphic
indicating radioactivity or radiation: actinometer
Word Origin
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
Cite This Source
Word Origin and History for actino-

before vowels actin-, word-forming element meaning "pertaining to rays," from Greek aktis (genitive aktinos) "ray, radiance;" perhaps cognate with Sanskrit aktuh "light, ray," Gothic uhtwo "dawn, daybreak," Lithuanian anksti "early."

Online Etymology Dictionary, © 2010 Douglas Harper
Cite This Source
actino- in Medicine

actino- or actin-
Actinic radiation: actinotherapy.

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

Word of the Day

Nearby words for actino-

Word Value for actino

Scrabble Words With Friends