The Collaborative International Dictionary of English v.0.48:

Turnip \Tur"nip\ (t[^u]r"n[i^]p), n. [OE. turnep; probably fr.
   turn, or F. tour a turn, turning lathe + OE. nepe a turnip,
   AS. n[=ae]pe, L. napus. Cf. Turn, v. t., Navew.] (Bot.)
   The edible, fleshy, roundish, or somewhat conical, root of a
   cruciferous plant (Brassica campestris, var. Napus); also,
   the plant itself. [Formerly written also turnep.]
   [1913 Webster]

   Swedish turnip (Bot.), a kind of turnip. See Ruta-baga.


   Turnip flea (Zool.), a small flea-beetle (Haltica,
      striolata syn. Phyllotreta striolata), which feeds upon
      the turnip, and often seriously injures it. It is black
      with a stripe of yellow on each elytron. The name is also
      applied to several other small insects which are injurious
      to turnips. See Illust. under Flea-beetle.

   Turnip fly. (Zool.)
   (a) The turnip flea.
   (b) A two-winged fly (Anthomyia radicum) whose larvae live
       in the turnip root.
       [1913 Webster]