Promastigotes

Etymology
Promastigotes

pro: "before" (from latin prō, meaning "before")

mastigote: "whip" (from greek μάστιξ (mastix), meaning "whip")

Explanation
Promastigotes are one of the stages in the life cycle of certain protozoa, such as Leishmania. In this life cycle, they have the beginnings (pro) of a flagellum, which looks like a whip (mastigote). This enables them to be motile. Contrast this with amastigotes, another point in their life cycle, where they have no ("a" greek prefix indicating negation) flagellum (mastigote), or a very small one. Amastigotes are not motile because of this lack of a proper flagellum.