Flagellum \Fla*gel"lum\, n.; pl. E. Flagellums, L. Flagella. [L., a whip. See Flagellate, v. t.]

1. (Bot.) A young, flexible shoot of a plant; esp., the long trailing branch of a vine, or a slender branch in certain mosses.

2. (Zo["o]l.)
   (a) A long, whiplike cilium. See Flagellata.
   (b) An appendage of the reproductive apparatus of the snail.
   (c) A lashlike appendage of a crustacean, esp. the terminal ortion of the antenn[ae] and the epipodite of the maxilipeds. See Maxilliped.

Source: Webster's Revised Unabridged Dictionary (1913)