'asteroidal' originates from the noun 'asteroid', which itself comes from Greek 'asteroeidēs', where 'aster-' meant 'star' and '-oeidēs' meant 'like' or 'in the shape of'; the adjectival English suffix '-al' was added to form 'asteroidal'.

'asteroidal' changed from the noun 'asteroid' (borrowed into English in the early 19th century from Greek 'asteroeidēs' via Neo-Latin), and the adjective developed in English from that noun to describe things like or relating to asteroids.

Initially it meant 'star-like' (resembling a star in appearance); over time it came to refer specifically to 'relating to or resembling an asteroid (a small rocky body in space)', the current primary sense.