actine
/ˈaktiːn/noun
1A proposed unit of the intensity of solar radiation. rare. Now historical.
2 Zoology. Each of the rays or points of a sponge spicule.
Origin
Mid 19th century; earliest use found in John Herschel (1792–1871), mathematician and astronomer. From ancient Greek ἀκτῖν-, ἀκτίς ray. With use in sense 1 compare quot. 1837, and also German †Actine.