Dictionary
actino-
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, esp. before a vowel,actin-.Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.