adiactinic,a.Chem.|ˌædɪækˈtɪnɪk| [f. a- prefix 14 + diactinic.] Not diactinic; not transmitting the chemical rays of light. 1880Nineteenth Cent. Mar. 529 Those substances which are chemically transparent are said to be diactinic; while those which are chemically opaque are, of course, adiactinic.