adjectival word-forming element, especially in zoology, "belonging to, connected with, member of a group or class," in some cases probably via from French -ide, back-formed from Modern Latin names of zoological classes in -idae, as arachnid "a spider" from the biological class name arachnidae.
This -idae is the plural of Latin -ides, a masculine patronymic (indicating "descent from"), from Greek -ides "son of," denoting descent from the person to whose name it is attached (such as Heraklides).
In astronomy, of meteor showers, "having its radiant in" the constellation named (Perseid, Leonid, etc.), it probably represents Latin -idis, from Greek -idos, the genitive of the feminine form of the patronymic suffix.
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<a href="https://www.etymonline.com/word/Cepheid">Etymology of Cepheid by etymonline</a>
Harper, D. (n.d.). Etymology of Cepheid. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Cepheid