English Alternative forms acontium Etymology From the plural of New Latin acontium, from Ancient Greek ἀκόντιον (akóntion, “little dart”). Noun acontia (plural acontias) (zoology) Threadlike defensive organs, composed largely of nettling cells (cnidae), thrown out of the mouth or special pores of certain Actiniae when irritated. Derived terms acontialWikiwand - on Seamless Wikipedia browsing. On steroids.