actino-

American  

1. 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 ).

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actino- British  

combining form

1. indicating a radial structure

   actinomorphic

2. indicating radioactivity or radiation

   actinometer

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Etymology

Origin of actino-

< Greek, combining form representing aktī́s (genitive aktînos ) ray, beam; -o-