Entry 1 sense Webster, 1913 Actinology · Ac·ti·nol·o·gy · IPA /ˌæk.tɪˈnɑ.lə.d͡ʒi/ 01 n. The science which treats of rays of light, especially of the actinic or chemical rays. 1. The science which treats of rays of light, especially of the actinic or chemical rays.